MEXICO CITY – Swine flu has infected Mexico’s relations with China and other countries that have canceled airline flights and halted some trade. But its most prickly neighbor — the United States — now seems like the country’s most loyal friend.

Mexico is smarting from what it considers discriminatory actions by countries it had considered friendly, insisting the world should be grateful for its open and aggressive efforts to stem the spread of swine flu. The shutdown of public life cost Mexico $2.2 billion in the first 10 days after the epidemic was announced.

The government sent a plane to pick up 70 of its citizens quarantined in China. It rebuked Cuba, Ecuador, Argentina and Peru for banning flights to Mexico, saying they were acting “incongruously with our traditional ties of friendship.”

France tried — and failed — to win a European Union-wide ban on flights to Mexico.

Particularly insulting for Mexico: Haiti rejected a Mexican ship last week carrying 77 tons of much-needed food aid because of swine flu fears.

All of that put the U.S. response in a very favorable light. Neither the United States nor Canada banned flights or restricted trade with Mexico. The three countries are partners in the North American Free Trade Agreement.

President Obama forcefully rejected the idea of closing the border, despite arguments from conservative talk show hosts that swine flu showed immigration from Mexico was a threat.

The Obama administration cast the decision as a recognition of reality: Homeland Security Secretary Janet Napolitano said sealing the border would be extremely costly and pointless since the virus was already in the United States. Obama likened the idea to “closing the barn door after the horses are out.”

Even so, it was symbolically significant in Mexico, which protested when the U.S. began building a border fence under former President George W. Bush.

While Obama has also beefed up border security, he has pledged to renew efforts to push through immigration reforms that eluded the Bush administration, including extending a citizenship path for illegal immigrants. His emphasis on open borders during the swine flu outbreak could help set the tone.

“There was a very explicit recognition that the U.S. and Mexico cannot close their borders,” said Andrew Selee, director of the Mexico Institute at the Washington-based Wilson Center. “Maybe that tells you that Mexico is really more integrated with its neighbors to the north than the rest of Latin America.”

Mexico took note. The Foreign Relations Department held a special ceremony to thank the U.S. government both for keeping the border open and for providing aid and medical expertise.

“The way in which the border between Mexico and the United States stayed not only open but alive in the past days has been exemplary,” said Carlos Rico, Mexico’s deputy secretary for North American relations. “The open border is something that has not been recognized enough.”

Even members of the opposition leftist Democratic Revolution Party — long known for its nationalistic wariness of the United States — were impressed.

“I thought the reaction and response from the three countries — Mexico, the United States and Canada — was definitely laudable,” said Alfonso Suarez de Real, a lawmaker from the party. “It contrasted with the reaction that other countries have had.”

The experience added momentum to increasingly warming relations, coming on the heels of Obama’s April 16 visit to Mexico and his acknowledgment that Americans share the blame for violence south of border because of drug consumption and gun trafficking. Mexico, for its part, has set aside traditional sovereignty concerns in welcoming increased U.S. border security and even U.S. training for Mexico’s navy.

In contrast, relations with China have been frayed, threatening to undermine trade and investment between the two countries just as it has been picking up, said Hector Cuellar, president of the recently formed Mexico-China Chamber of Commerce.

Prominent Mexican companies have started opening operations in China in the last three years, while Mexican exports to China have jumped ninefold over the past decade to some $2 billion.

But Mexicans were angered when China banned the direct flights that leading Mexican airline Aeromexico started offering in October, and then quarantined Mexican travelers. Mexico canceled its participation at a Shanghai trade fair where it had meant to showcase its pork products — now banned in China and at least four other nations even though health experts say people can’t catch swine flu from meat.

The epidemic also set back Mexico’s efforts to improve ties with Cuba, which soured during the 2000-06 presidency of Vicente Fox, when Mexico voted at the U.N. in favor of monitoring human rights on the communist island.

Fox’s successor, Felipe Calderón, had planned a conciliatory trip to Cuba this year. That’s up in the air after Calderon said he may have to cancel because Cuba grounded flights to and from Mexico.

Mexican officials also didn’t take kindly to Fidel Castro lashing out after Cuba confirmed its first swine flu case, accusing Mexico of waiting to disclose the epidemic until after Obama visited, even though Canadian and U.S. scientists did not identify the virus in Mexican patients until a week later.

In Europe for a summit Tuesday, Foreign Relations Secretary Patricia Espinosa told Cuba’s foreign relations minister, Bruno Rodriguez, that such remarks “hurt bilateral relations.”

Deputy Health Secretary Mauricio Hernandez said Wednesday that Mexico would support a global compensation fund for countries that suffer from epidemics, and warned that the threat of trade and travel restrictions could provoke governments to hide future outbreaks.

“We were responsible, and we ended up with trade sanctions — we were discriminated against,” Hernandez said at an academic forum on swine flu. “So, the question is: What is the incentive (for countries to be open)?”

LONDON – As swine flu cases hit 6,500 worldwide, World Health Organization officials were meeting with vaccine manufacturers and other experts in Geneva on Thursday to discuss making a vaccine to fight the virus.

The meeting focused on the major questions surrounding a possible swine flu vaccine, such as how much should be produced, how it will be distributed and who should get it.

The expert group’s recommendations will be passed to WHO Director-General Margaret Chan, who will issue advice to vaccine manufacturers and the World Health Assembly next week.

But some experts feel the main decision has already been made.

“It’s a foregone conclusion,” said David Fedson, a vaccines expert and former professor of medicine at the University of Virginia. “If we don’t invest in an H1N1 (swine flu) vaccine, then possibly we could have a reappearance of this virus in a mild, moderate, or catastrophic form and we would have absolutely nothing.”

Flu vaccine companies can only make one vaccine at a time: seasonal flu vaccine or pandemic vaccine. Production takes months and it is impossible to switch halfway through if health officials make a mistake.

Vaccine makers can make limited amounts of both seasonal flu vaccine and pandemic vaccine — though not at the same time — but they cannot make massive quantities of both because that exceeds manufacturing capacity.

Seasonal flu kills up to 500,000 people a year. At the moment, health officials aren’t sure how deadly swine flu is, and whether they will need more seasonal flu vaccine or swine flu vaccine. And if the swine flu mutates, scientists aren’t sure how effective a vaccine made now from the current strain will remain.

WHO estimates that 1 to 2 billion doses of swine flu vaccine could be produced every year, though the first batches wouldn’t be available for 4 to 6 months.

The U.S. Centers for Disease Control and Prevention is currently working on a “seed stock” to make the vaccine, which should be ready in the next couple of weeks. That will be distributed to manufacturers worldwide so they can start producing the vaccine.

WHO is also negotiating with vaccine producers to save some of their swine flu vaccine for poorer nations. Many rich nations like Britain, Canada, Denmark, France, Switzerland and the United States signed deals with vaccine makers years ago to guarantee them pandemic vaccines as soon as they’re available.

As of Thursday, at least 33 countries reported nearly 6,500 cases of swine flu worldwide, with 65 deaths. According to WHO’s pandemic alert level, the world is at phase 5 — out of a possible 6 — meaning that a global outbreak is “imminent.”

“It’s a no-brainer,” Fedson said of the decision to make swine flu vaccine. “All that’s being discussed now is the details of how to make sure you have enough seasonal flu vaccine and the logistics of making the switch to H1N1 vaccine production.”

North America has been the hardest-hit continent. The United States has reported 3,352 laboratory-confirmed cases of swine flu, including three deaths. Mexico has 2,446 cases and 60 deaths, while Canada has 389 cases with one death, according to WHO figures.

Spain and Britain have the most cases in Europe, at 100 and 71 respectively.

In Central America, Costa Rica has eight cases and one death and Panama has 29 cases.

HAVANA – Fidel Castro accused Mexico of failing to disclose the spread of swine flu until after U.S. President Barack Obama had visited, as Cuba confirmed its first case of the virus in a Mexican medical student studying on the island.

The Health Ministry said the “young male” became ill during a vacation in Mexico and returned to his studies at a medical clinic in Matanzas province, east of Havana. A statement read on state television Monday night gave no details on his current condition.

Castro, the former Cuban president, reacted hours later, writing in a column posted on a government Web site that “Mexican authorities did not inform the world of the presence (of swine flu), while they waited for Obama’s visit.”

Obama stopped in Mexico en route to the Summit of the Americas in Trinidad last month, days before Mexican health officials closed schools and announced swine flu was spreading, prompting an eventual mass shutdown that brought many parts of the country to a virtual halt.

The Cuban Health Ministry statement said a group of Mexican students began arriving on April 25 — four days before Cuban authorities halted airline flights to and from Mexico to keep swine flu from spreading to the island.

Relations between Cuba and Mexico have been chilly for several years, since a diplomatic spat involving the government of then-President Vicente Fox. Mexican authorities had said Fox’s successor, Felipe Calderon, would visit the island during the first quarter of 2009 as part of an ongoing effort to improve ties.

But Calderon recently said he may have to delay plans for a Cuba visit, quipping that the island’s grounding of flights to and from Mexico may leave him with no way to make the trip.

Cuba’s 82-year-old former president blasted Calderon for that comment and chided Mexican authorities for failing to disclose the spread of swine flu sooner.

“At this moment, we and dozens of other countries are paying the consequences and, on top of that, they accuse us of taking hurtful measures toward Mexico.”

He added that the measures that the Mexican president was complaining about “met established norms and had not even the slightest intention of affecting the brother country of Mexico.”

In its statement Monday, Cuba’s Health Ministry said other Mexican medical students returning from vacation at the same time as the young man diagnosed with swine flu experienced cold symptoms and were quarantined for observation, but most were deemed healthy and released.

Tests by the Institute of Tropical Medicine in Havana confirmed the first case of swine flu, though it was unclear how many Mexican students might still be isolated for more testing.

The ministry said that in all of Cuba, authorities tested 84 possible cases in people of eight nationalities and had only found the one positive result.

The official ban on flights between Mexico and Cuba has since been eased to allow Cuba’s national airline to send a few planes a week to pick up its citizens in Mexico. Still, several flights a day between Havana and the resort of Cancun or Mexico City continue to be canceled, stranding hundreds of passengers.

A study published Monday in the journal Science estimated Mexico alone may have had 23,000 cases by April 23, the day it announced the epidemic. The study estimates swine flu kills between 0.4 percent and 1.4 percent of its victims, but lead author Neil Ferguson of Imperial College, London, said the data remain incomplete.

The number of countries reporting swine flu cases stands at 31, with the World Health Organization confirming about 4,800 cases. At least 61 people have been killed by swine flu around the world: 56 in Mexico, three in the U.S., one in Canada and one in Costa Rica.

MEXICO CITY – The swine flu virus spread to more countries Tuesday as scientists estimated the new strain could have sickened 23,000 people in Mexico alone before anyone realized it was an epidemic.

Fidel Castro, meanwhile, accused Mexico of hiding the epidemic until after President Barack Obama visited last month.

Mexican Health Secretary Jose Cordova said his nation’s shutdown of schools — which was lifted in most of the country’s 31 states Monday — had averted an avalanche of cases.

“It would have been difficult for us to have controlled this epidemic,” Cordova said in a statement, adding that Mexico had 56 deaths and 2,059 confirmed cases of swine flu.

But Castro, the former Cuban president, accused Mexico of failing to disclose the spread of swine flu until after Obama had visited en route to the Summit of the Americas in Trinidad last month.

“Mexican authorities did not inform the world of the presence (of swine flu), while they waited for Obama’s visit,” he wrote on a government Web site hours after Cuba confirmed its first swine flu case.

Obama’s April 16 visit came a week before Mexican health officials announced swine flu was spreading, prompting an eventual mass shutdown that brought many parts of the country to a virtual halt.

Thailand and Finland reported their first confirmed swine cases Tuesday of people just arrived from Mexico. Cuba and China — both countries that had imposed strict measures on flights and travelers from Mexico — also reported their first confirmed cases.

Cuba identified its patient as a Mexican student attending a Cuban medical school and China said its case involved a Chinese student who had just returned from the United States.

At least 61 people have been killed by swine flu around the world, and the World Health Organization has confirmed over 5,250 cases.

Cuba’s Health Ministry said a group of medical students from Mexico began arriving on the island to resume their studies April 25 — four days before Cuban authorities halted airline flights from Mexico. Fourteen of the students suffered from flu-like symptoms.

A study published Monday in the journal Science estimated Mexico alone may have had 23,000 cases of swine flu by April 23, the day it announced the epidemic. The study estimates swine flu kills between 0.4 percent and 1.4 percent of its victims, but lead author Neil Ferguson of Imperial College, London, said the data remain incomplete.

“It’s very difficult to quantify the human health impact at this stage,” he said.

The analysis in Science suggests there are many more cases than those confirmed by laboratories — anywhere from 6,000 to 32,000 cases in Mexico as of April 23. The flu has since spread around the world, and the study said it appears to be substantially more contagious than normal, seasonal flu.

Researchers also compared the genetic sequences of the viruses in 23 confirmed cases, and came up with an estimate of Jan. 12 for their earliest common ancestor — presumably when person-to-person transmission began. But they said it could have been anywhere from Nov. 3 to March 2.

The researchers said the 2009 H1N1 flu appears to be about equal in severity to the flu of 1957 and less severe than the deadly 1918 version.

In Mexico, Monday’s reopening of kindergartens and primary and middle schools shut since April 24 was the latest step in efforts to restore a sense of normality. Businesses, government services, high schools and universities reopened last week.

But six of Mexico’s 31 states put off reopening schools for a week because of local rises in the number of flu cases, and a seventh pushed it back a day to Tuesday. The Education Department said it will tack an extra seven days onto the school calendar to make up for the lost time.

But while officials praised the health and education systems for their response to the crisis, there were signs that Mexico’s overburdened health system was under strain.

Dozens of government health care workers, including doctors and nurses, marched and blocked streets in the Gulf coast city of Jalapa to demand higher pay and better working conditions.

“The government asked our help in combatting the influenza epidemic, now we are asking the government to do us justice,” said nurse Mariana Cortes, one of the protest organizers.

Mexico is trying to revive its economy after the epidemic pummeled tourism, the country’s third-largest source of legal foreign income. Mexico provided details Monday of a $1.1 billion package to help restaurants, hotels and other businesses.

At least 10 commercial banks are involved in the plan, promising three-month reprieves for small businesses with outstanding loans in Mexico City and two hard-hit states. Small businesses in beach resorts and other tourist destinations were promised a six-month grace period.

Later in the day, Tourism Secretary Rodolfo Elizondo said the government would launch a $90 million publicity campaign this week urging Mexicans to vacation at home.

Noting that several nations have issued travel warnings or restricted airline flights to Mexico, Elizondo said trying to promote trips to Mexico by foreigners now “would be like throwing money away.”

With Cuba, Thailand and Finland reporting their first cases, the number of countries reporting confirmed swine flu cases grew to 33. The United States has the most confirmed cases — 2,618 — according to the U.S. Centers for Disease Control and Prevention. Swine flu has killed 56 people in Mexico, three in the U.S., one in Canada and one in Costa Rica.

Associated Press writers Miguel Angel Hernandez in Veracruz, Maria Cheng in London, Randolph E. Schmid in Washington and Gillian Wong in Beijing contributed to this report.

By Mark Stevenson, David Koop

CHICAGO – Did government health officials “cry swine” when they sounded the alarm on what looked like a threatening new flu?

The so-far mild swine flu outbreak has many people saying all the talk about a devastating global epidemic was just fear-mongering hype. But that’s not how public health officials see it, calling complacency the thing that keeps them up at night.

The World Health Organization added a scary-sounding warning Thursday, predicting up to 2 billion people could catch the new flu if the outbreak turns into a global epidemic.

Many blame such alarms and the breathless media coverage for creating an overreaction that disrupted many people’s lives.

Schools shut down, idling even healthy kids and forcing parents to stay home from work; colleges scaled back or even canceled graduation ceremonies; a big Cinco de Mayo celebration in Chicago was canned; face masks and hand sanitizers sold out — all because of an outbreak that seems no worse than a mild flu season.

“I don’t know anyone who has it. I haven’t met anyone who knows anyone who contracted it,” said Carl Shepherd, a suburban Chicago video producer and father of two. “It’s really frightening more people than it should have. It’s like crying wolf.”

Two weeks after news broke about the new flu strain, there have been 46 deaths — 44 in Mexico and two in the United States. More than 2,300 are sick in 26 countries, including about 900 U.S. cases. Those are much lower numbers than were feared at the start based on early reports of an aggressive and deadly flu in Mexico.

Miranda Smith, whose graduation ceremony at Cisco Junior College in central Texas was canceled to avoid spreading the flu, blames the media.

“It’s been totally overblown,” she said Thursday.

“Everyone seems to know it’s not going to kill you and it’s not as deadly as they think,” she said. “Everybody needs to just calm down and chill out.”

Craig Heyl of Decatur, Ga., said the government overreacted.

“Swine flu is just another strain of flu. People get the flu. I guess you have to call it a pandemic when it’s a widespread virus, but I don’t think the severity of it is all that concerning,” said Heyl, 43.

Public health authorities acknowledge their worst fears about the new virus have not materialized. But no one’s officially saying it’s time to relax. And experts worry that people will become too complacent and tune out the warnings if the virus returns in a more dangerous form in the fall.

“People are taking a sigh of relief too soon,” said Dr. Richard Besser, acting director of the Centers for Disease Control and Prevention.

In an interview Wednesday with The Associated Press, Besser said the outbreak in the United States appears to be less severe than was first feared. But the virus is still spreading and its future potential as a killer is not clearly understood.

“The measures we’ve been talking about — the importance of handwashing, the importance of covering coughs, the real responsibility for staying home when you’re sick and keeping your children home when you’re sick — I’m afraid that people are going to say, ‘Ah, we’ve dodged a bullet. We don’t need to do that,”‘ Besser said.

“The thing that’s keeping me up right now is that feeling of dodging the bullet,” he added.

Peter Sandman, a risk communication specialist, says on his Web site that reminding people the risk is still real and warning them in the future if a pandemic looks imminent “will be extremely difficult.”

“Swine flu looks to be an extremely mild pandemic if it goes pandemic at all, despite WHO warnings that it may ‘come back with a vengeance’ in the fall. People are going to be very, very skeptical,” Sandman wrote.

That concern is shared by infectious disease specialists. But elsewhere, especially online, talk of hype is rampant.

“If I hear 1+ person freaking out because of the “Swine Flu” they won’t have 2 worry about dying from it. I will kill them w/ my handbag!” read a comment Wednesday on Twitter.

“Adults are acting like a bunch of crybabies in a B-rated science fiction germ-outbreak movie, wringing their hands, whining about what to do next,” Dallas Morning News reader Mark Thompson wrote in a letter to the editor posted online Wednesday.

Kari Carsey Valente of Lake Oswego, Ore., had similar thoughts in a letter on the Oregonian newspaper’s Web site.

“Is the daily front page body count really necessary? In reading the entire content of the collected articles one learns that the H1N1 strain is not likely to be more lethal than its predecessors. Give it a rest — and lots of liquid!,” Valente wrote.

Colt Ables, 22, an economics major at the University of Texas in Arlington, said he thinks the Obama administration overreacted and unfairly tried to make it seem as if Republicans have been soft on preparedness.

“This shouldn’t be about politics or about hyping up a virus to send the American people into a panic. Do yourself a favor, wash your hands and turn off the TV,” he wrote in a campus newspaper column.

Whether the media overhyped or accurately reported the dangers is a toss-up, according to a USA Today/Gallup poll published Thursday on Americans’ views of the media’s flu coverage.

The May 5 poll also found that concern about the flu peaked a week ago. But even then, only 25 percent of Americans said they worried about getting the virus.

Dr. Robert Daum, a University of Chicago infectious disease expert, says authorities acted properly when news first broke about the new flu strain.

“It’s like overcalling a snowstorm in Chicago. You want the plows out even if it’s only going to snow a flake,” Daum said. If not, and a blizzard hits, “there will be an outcry like you’ve never seen before.”

Still, Daum says authorities have been a bit awkward in “downshifting” now that it appears the U.S. situation isn’t dire.

“I think it was right to place everyone on high alert, and now right” to say it’s time to calm down, Daum said.

By Mike Stobbe, Lindsey Tanner

MEXICO CITY – Bird flu kills more than 60 percent of its human victims, but doesn’t easily pass from person to person. Swine flu can be spread with a sneeze or handshake, but kills only a small fraction of the people it infects.

So what happens if they mix?

This is the scenario that has some scientists worried: The two viruses meet – possibly in Asia, where bird flu is endemic – and combine into a new bug that is both highly contagious and lethal and can spread around the world.

Scientists are unsure how likely this possibility is, but note that the new swine flu strain – a never-before-seen mixture of pig, human and bird viruses – has shown itself to be especially adept at snatching evolutionarily advantageous genetic material from other flu viruses.

“This particular virus seems to have this unique ability to pick up other genes,” said leading virologist Dr. Robert Webster, whose team discovered an ancestor of the current flu virus at a North Carolina pig farm in 1998.

The current swine flu strain – known as H1N1 – has sickened more than 2,300 people in 24 countries. While people can catch bird flu from birds, the bird flu virus – H5N1 – does not easily jump from person to person. It has killed at least 258 people worldwide since it began to ravage poultry stocks in Asia in late 2003.

The World Health Organization reported two new human cases of bird flu on Wednesday. One patient is recovering in Egypt, while another died in Vietnam – a reminder that the H5N1 virus is far from gone.

“Do not drop the ball in monitoring H5N1,” WHO Director-General Margaret Chan told a meeting of Asia’s top health officials in Bangkok on Friday by video link. “We have no idea how H5N1 will behave under the pressure of a pandemic.”

Experts have long feared that bird flu could mutate into a form that spreads easily among people. The past three flu pandemics – the 1918 Spanish flu, the 1957-58 Asian flu and the Hong Kong flu of 1968-69 – were all linked to birds, though some scientists believe pigs also played a role in 1918.

Webster, who works at St. Jude’s Children’s Research Hospital in Memphis, Tenn., said bird flu should be a worry now. Bird flu is endemic in parts of Asia and Africa, and cases of swine flu have already been confirmed in South Korea and Hong Kong.

“My great worry is that when this H1N1 virus gets into the epicenters for H5N1 in Indonesia, Egypt and China, we may have real problems,” he told The Associated Press. “We have to watch what’s going on very diligently now.”

The U.S. Centers for Disease Control and Prevention are extraordinarily busy trying to understand the swine flu virus itself, and haven’t had time to break off staff to look at the possibility of a swine flu-bird flu mix, spokesman Dave Daigle said.

Malik Peiris, a flu expert at Hong Kong University, said the more immediate worry is that swine flu will mix with regular flu viruses, as flu season begins in the Southern Hemisphere. It is unclear what such a combination would produce.

But he said there are indications that scenario is possible. Peiris noted that the swine flu virus jumped from a farmworker in Canada and infected about 220 pigs. The worker and the pigs recovered, but the incident showed how easily the virus can leap to a different species.

“It will get passed back to pigs and then probably go from pigs to humans,” Peiris said. “So there would be opportunities for further reassortments to occur with viruses in pigs.”

He said so far bird flu hasn’t established itself in pigs – but that could change.

“H5N1 itself has not got established in pigs,” he said. “If that were to happen and then these two viruses were both established in pigs in Asia, that would be quite a worrying scenario.”

Michael Osterholm, an infectious disease specialist at the University of Minnesota who has advised the U.S. government on flu preparations, said while flu experts are discussing the scenario, he has yet to see specific evidence causing him to think it will happen.

“Everything with influenza is a huge guessing game because Mother Nature holds all the rules, and we don’t even know what they are, so anything’s possible,” he said. “We don’t have any evidence that this particular reassortment is that much more likely to pick up H5N1 than any other reassortment out there.”

“We don’t have to put these things together,” he added. “This is not chocolate and peanut butter running into each other in the dark hallway.”

But there is in fact discussion of putting them together – in a high-security laboratory – to see what a combination would look like, according to Webster. Similar tests have been done at the CDC mixing bird flu and seasonal human flu, resulting in a weak product, he said.

Daigle, the CDC spokesman, said the agency wants to look at the question in the future.

Webster has done groundbreaking work on both swine and bird flus in his 40-year career, and has followed the evolution of the current swine flu strain from a virus that sickened a handful of people who worked with North Carolina hogs into a bug that has spread from person to person around the world.

He is closely involved in the global effort to analyze what the virus might do next. It has killed 42 people in Mexico and two in Texas, but so far has not proven very deadly elsewhere, leading to some criticism that the World Health Organization’s warnings of a potential pandemic have been overblown.

Webster said underestimating the swine flu virus would be a huge mistake.

“This H1N1 hasn’t been overblown. It’s a puppy, it’s an infant, and it’s growing,” he said. “This virus has got the whole human population in the world to breed in – it’s just happened. What we have to do is to watch it, and it may become a wimp and disappear, or it may become nasty.”

AP Medical Writer Maria Cheng in London contributed to this report.

GENEVA – Up to 2 billion people could be infected by swine flu if the current outbreak turns into a pandemic lasting two years, the World Health Organization said Thursday.

WHO flu chief Keiji Fukuda said the historical record of flu pandemics indicates one-third of the world’s population gets infected in such outbreaks. Independent experts agreed that the estimate was possible.

In Mexico, the hardest hit country so far, high schools and universities opened for the first time in two weeks as the government’s top health official insisted the epidemic is on the decline. All students were checked for swine flu symptoms and some were sent home.

“If we do move into a pandemic, then our expectation is that we will see a large number of people infected worldwide,” Fukuda said. “If you look at past pandemics, it would be a reasonable estimate to say perhaps a third of the world’s population would get infected with this virus.”

With the current total population of more than 6 billion, that would mean an infection total of 2 billion, he said, but added that the world has changed since pandemics of earlier generations, and experts are unable to predict if the impact will be greater or smaller.

“We don’t really know.” said Fukuda. “This is a benchmark from the past. Please do not interpret this as a prediction for the future.”

Chris Smith, at flu virologist at Cambridge University in England, said the 2 billion estimate was possible.

“That doesn’t sound too outlandish to me for the simple reason that this is a very infectious virus,” Smith told The Associated Press. “You’re talking about a virus that no one in the population has seen before and therefore everyone is immunologically vulnerable. Therefore it’s highly likely that once it starts to spread, people will catch it. And since the majority of the world’s population are in contact with one another, you’re going to get quite a lot of spread.”

John Oxford, professor of virology at St. Bart’s and Royal London Hospital, agreed.

“I don’t think the 2 billion figure should scare people because it’s not as though 2 billion people are going to die. The prediction from WHO is that 2 billion people might catch it. Half of those people won’t show any symptoms. Or if they show any symptoms, they will be so mild they will hardly know they’ve had it.”

Fukuda said it also is impossible to say if the current strain of swine flu will become severe or mild, but that even with a mild flu, “from the global perspective there are still very large numbers of people who could develop pneumonia, require respirators, who could die.”

A mild outbreak in wealthier countries can be “quite severe in its impact in the developing world,” Fukuda said.

People react differently to the flu depending on their general state of health and other factors, he said. Some younger people in the Southern Hemisphere may be more vulnerable because of poor diet, war, HIV infections and other factors.

“We expect this kind of event to unfold over weeks and months,” Fukuda said. “Really if you look over a two-period that is really the period in which you see an increase in the number of illnesses and deaths during a pandemic influenza.”

So far the swine flu virus has spread to 24 countries.

Mexican dance halls, movie theaters and bars were allowed to fully reopen Thursday after a five-day shutdown designed to curb the virus’ spread. Businesses must screen for any sick customers, and restaurant employees must wear surgical masks.

Fans can attend professional soccer matches this weekend after all were played in empty stadiums last weekend.

Mexico confirmed two more deaths, for a total of 44, while 1,160 people have been sickened, up 90 from Wednesday. Despite death tolls and confirmed caseloads that rise daily, Health Secretary Jose Angel Cordova insisted the epidemic is waning in Mexico.

WHO raised its global total of laboratory-confirmed cases to 2,099, from 1,893 late Wednesday, and said swine flu also has caused two deaths in the United States.

This swine flu seems to have a long incubation period — five to seven days before people notice symptoms, according to Dr. Marc-Alain Widdowson, a medical epidemiologist from the U.S. Centers for Disease Control and Prevention now tracking the flu in Mexico City. That means the virus can keep being spread by people who won’t know to stay home.

Laughing and joking, high school students gathered at the entrance of the National School of Graphic Arts in Mexico City, waiting to fill out forms that asked about their health.

Of 280 students entering the school in the first 20 minutes, two showed symptoms of swine flu, including coughing and nasal congestion, said assistant principal Ana Maria Calvo Vega. Their parents were notified and they won’t be readmitted without a statement from a doctor saying they don’t have the virus, she said.

Students at a Mexico City vocational high school were welcomed with a hand sanitizer and a surgical mask. Joyful to see each other again, students embraced and kissed — some through masks.

But some worried that the virus could surge back once young people gather in groups again.

“My 17-year-old daughter is afraid. She knows she must go back but doesn’t want to,” said Silvia Mendez as she walked with her 4-year-old son, Enrique, in San Miguel Topilejo, a town perched in forested mountains near the capital.

Working parents have struggled to provide child care during the shutdown. It forced many to stay home from work, bring their youngsters to their jobs, or leave them at home.

Each school, Mexican officials said, had to be cleaned and inspected this week. Complicating the task: Many schools are primitive buildings with dirt floors and lack proper bathrooms. It was unclear how students attending those schools could adhere to the government’s strict sanitary conditions.

The government promised detergent, chlorine, trash bags, anti-bacterial soap or antiseptic gel and face masks to state governments for delivery to public schools. But some local districts apparently didn’t get the word.

U.S. health officials are no longer recommending that schools close because of suspected swine flu cases since the virus has turned out to be milder than initially feared. But many U.S. schools have done so anyway, including the school of a Texas teacher who died.

In Asia, top health officials said the region must remain vigilant over the threat of swine flu, stepping up cooperation to produce vaccines and bolstering meager anti-viral stockpiles.

The virus has so far largely spared Asia. Only South Korea and Hong Kong have confirmed cases. On Thursday, China and Hong Kong released dozens of people quarantined over suspected contact with one of the region’s few swine flu carriers.

Past experience has been the spur to WHO to make sure the world is as prepared as possible for a pandemic, which would be indicated by a rise to phase 6 from the current phase 5 in the agency’s alert scale. That would mean general spread of the disease in another region beyond North America, where the outbreak so far has been heaviest.

“I’m not quite sure we know if we’re going to phase six or not or when we would do so,” Fukuda said. “It’s really impossible for anybody to predict right now.”

Officials said the agency was likely to shorten its annual meeting of its 193 member states later this month from 10 days to five because of the outbreak, which it was scheduled to discuss.

“That is under consideration,” Fukuda said. “Sure it is possible.”

Contributions from AP Medical Writer Maria Cheng in London and Associated Press writers Andrew O. Selsky in Mexico City and Michael Casey in Bangkok.

By Alexander G. Higgins, Eliane Engeler

MEXICO CITY – High schools and universities closed by the swine flu epidemic reopened across Mexico on Thursday as teachers and parents carefully checked returning students for flu symptoms.

Mexico had mobilized teachers and parents to disinfect its schools following a two-week closure intended to curb the spread of the virus. Some youths showing flu symptoms were sent home Thursday. Primary schools will reopen next week.

All places of business — including sports arenas, dance halls, movie theaters and restaurants — were allowed to reopen Thursday after a government-ordered shutdown that began last week.

But establishments must follow hygiene rules, including screening for any sick people, and make surgical masks mandatory for employees.

Secretary of Public Education Alonso Lujambio had called on citizens to show “strength of spirit,” trying to assuage worries that it was too early to restart classes after the flu killed 42 people in Mexico and sickened more than 1,100.

Laughing and joking, high school students gathered at the entrance of the National School of Graphic Arts in Mexico City, waiting to fill out forms that asked about their physical conditions.

Of 280 students entering the school in the first 20 minutes, two showed symptoms of swine flu, including coughing and nasal congestion, said assistant principal Ana Maria Calvo Vega. Their parents were notified and they won’t be readmitted without a statement from a doctor saying they don’t have the virus, she said.

“We’ll be observing these kids all day,” Calvo said. “We have to accept that this illness exists and be careful.”

Parents expressed relief that their children, shuttered too long in homes, could return to class. But they also worried that the virus could surge back once 40 million young people gather in groups again.

“My 17-year-old daughter is afraid. She knows she must go back but doesn’t want to,” said Silvia Mendez as she walked with her 4-year-old son, Enrique, in San Miguel Topilejo, a town perched in forested mountains near the capital.

Mendez and her son wore masks as they headed to the tiny roasted chicken restaurant she owns. Enrique spoke adoringly of his teacher and seemed impatient to get back to kindergarten.

Working parents have struggled to provide child care during the shutdown. It forced many to stay home from work, bring their youngsters to their jobs, or leave them at home.

Isabel Garcia had to leave her 11-year-old son, Charlie, behind while she sold vegetables below a red-domed church in San Miguel Topilejo’s central plaza.

“I’m nervous about him going back to school on Monday. But he will wear a mask and I have instructed him to stay away from any children who appear sick,” Garcia said at her stall, a colorful tableau of radishes, carrots, green onions and other fresh produce.

This swine flu seems to have a long incubation period — five to seven days before people notice symptoms, according to Dr. Marc-Alain Widdowson, a medical epidemiologist from the U.S. Centers for Disease Control and Prevention now tracking the flu in Mexico City. That means the virus can keep being spread by people who won’t know to stay home.

Government-mandated “filter” teams, composed of parent volunteers and school officials, will check returning students for any respiratory ailments.

“If the least suspicion exists, the boy or girl can’t remain and the Health Department will be notified,” said Cecilia Landerreche Gomez Morin, director-general of Mexico’s Family Welfare Agency.

The government also created an online manual, “What to do to restart classes without risk?” It calls for parents and school employees to clean classrooms, cafeterias and other areas with water, soap and chlorine, and to provide running water for hand-washing.

Each school, Mexican officials said, must be cleaned and inspected this week. Complicating the task: Many schools are primitive buildings with dirt floors and lack proper bathrooms. It was unclear how students attending those schools could adhere to the government’s strict sanitary conditions.

The government promised detergent, chlorine, trash bags, anti-bacterial soap or antiseptic gel and face masks to state governments for delivery to public schools. But some local districts apparently didn’t get the word.

Guillermo Narro Garza, acting secretary of education for Ciudad Juarez, along the border with Texas, said only chlorine would be used — and that parents have to supply it.

Mexico’s public education department said students must complete the yearly requirement of 800 hours in class, but did not say if the term would be extended because of the shutdown.

U.S. health officials are no longer recommending that schools close because of suspected swine flu cases since the virus has turned out to be milder than initially feared. But many U.S. schools have done so anyway, including the school of the Texas teacher who just died.

Deaths have slowed as the country mobilized an aggressive public health response to the epidemic that has sickened thousands in 24 countries. Sweden and Poland were the latest countries to confirm swine flu cases, both in women who had recently visited the U.S.

In San Diego, Calif., the U.S. Navy canceled the deployment of the USS Dubuque, an amphibious transport ship, after a crew member was confirmed to have swine flu. About 50 others were suspected cases, and all crew members were being treated with antiviral drugs.

In Washington, CDC officials said they identified genetic characteristics of the virus and were in position to produce a vaccine if one is needed.

Canada, meanwhile, said researchers at the National Microbiology Laboratory in Winnipeg, Manitoba, genetically sequenced three samples of the virus from Mexico and Canada, a breakthrough they hope will answer questions about how it spreads and mutates.

MEXICO CITY – Dozens of Mexican nationals quarantined in China despite having no swine flu symptoms arrived home Wednesday on a government-chartered jet, some complaining of “humiliation and discrimination” by the Chinese. But as Mexicans emerged from their own five-day swine flu shutdown, the death toll rose and many remained fearful.

Mexico City showed more of its usual ebullience during a raucous morning rush hour. Thousands of newspaper vendors, salesmen hawking trinkets and panhandlers dropped their protective masks and added to the familiar din of truck horns and street music. Cafes accepted sitting customers, and many corporate offices reopened.

Construction worker Roberto Reyes, 36, walked through the capital’s Chapultepec subway station without a protective mask.

“The news says all of this is over, so I got rid of my mask, and a lot of people are doing the same in the streets,” he said.

Many others worried about Mexico letting its guard down too quickly, especially with high schools and universities reopening Thursday, and primary schools reopening next week.

Mexico’s shutdown was designed to reduce the spread of the virus at its epicenter, and deaths did slow as the country mobilized an aggressive public health response to the epidemic that has gone on to sicken nearly 1,900 people in 21 countries.

But the virus keeps setting off more health alarms. A pregnant 33-year-old teacher in Texas who fell into a coma and had her baby delivered by Cesarean section became the first U.S. resident to die of swine flu. And Mexico announced a jump in the confirmed death toll Wednesday to 42 after testing backlogged cases.

Two of those deaths were from Tuesday. While the rate of new cases and hospitalizations has declined, epidemiologists said the virus has spread throughout Mexico. “We have seen a tendency (of the outbreak) to diminish, but not disappear,” Health Secretary Jose Angel Cordova said.

The Texas woman had chronic medical conditions, as did a Mexico City toddler who died of swine flu last week during a visit to Houston, health officials said. Her district said it would close schools until Monday as a precaution.

Mexico criticized China’s quarantine of its citizens as discriminatory, and First lady Margarita Zavala was up before dawn to greet the 136 passengers at Mexico City’s international airport. Authorities said 72 had been in Shanghai, 18 in Beijing, 34 in Guangzhou and 12 in Hong Kong. None had flu symptoms, Mexican diplomats said.

“It was discrimination and humiliation in my case,” said Myrna Berlanga, who said she was taken off a flight from the United States by Chinese officials and put in a mobile laboratory for five hours without food, water or a bathroom. “They took me out because of my passport,” she said.

Maria Lourdes Castaneda traveled to Hong Kong for a trade show. “Nobody wanted to give us a hotel room,” she said. “The manager of the Ramada kicked us out and told us there weren’t any rooms.”

Several other Mexican passengers said they were treated well despite being quarantined for four days.

China has defended its measures to block the virus from entering the world’s most populous nation and says it will continue strident checks on travelers from regions hit by swine flu. Its foreign ministry denied singling out Mexicans and said it hoped Mexico would “address the issue in an objective and calm manner.”

China had earlier canceled the only direct flights between China and Mexico, a twice weekly service by Aeromexico.

“This is purely a question of health inspection and quarantine,” ministry spokesman Ma Zhaoxu said Monday.

Lin Ji, a health official with China’s health department in Jilin province, said the government had decided to lift a quarantine for a group of Canadian students two days early, following pressure from Canada.

In Hong Kong, 34 passengers who arrived on a flight from Shanghai with a Mexican swine flu patient April 30 will be released from quarantine Thursday, Secretary for Food and Health York Chow said. Their nationalities weren’t immediately clear.

Doctors were still running tests on the Mexican patient. Chow said he was in stable condition.

Dr. David Nabarro, senior U.N. coordinator for influenza, said countries must explain to WHO their rationale for quarantines and trade restrictions, saying their effectiveness is minimal at best.

“We want to be very clear that the World Health Organization is not recommending travel restrictions related to the outbreak of this novel influenza,” Nabarro said.

Elsewhere Wednesday, Swedish authorities confirmed the Scandinavian country’s first swine flu case — a woman who recently visited the United States. The Swedish Institute for Infectious Disease Control said the woman, in her 50s, has recovered.

Before the Mexican nationals came home, about 20 Chinese businessmen and students, each wearing surgical masks, left the border city of Tijuana on a Chinese government flight. They had been stranded when China canceled all direct flights to Mexico.

Mexico’s government had imposed the five-day shutdown to curb the flu’s spread, particularly in this metropolis of 20 million where the outbreak sickened the most people. Capital residents overwhelmingly complied — other towns less — and government officials hailed the drastic experiment as a success.

Some, however, again urged caution. “We can’t make a prediction of what’s going to happen,” said Dr. Ethel Palacios, deputy director of the swine flu monitoring effort in Mexico City.

Mexican Finance Secretary Agustin Carstens unveiled plans Tuesday to stimulate key industries and fight foreign bans on Mexican pork products. He said persuading tourists to come back is a top priority.

Carstens said the outbreak cost Mexico’s economy at least $2.2 billion, and he announced a $1.3 billion stimulus package, mostly for tourism and small businesses, the sectors hardest hit by the epidemic.

The World Health Organization said it was shipping 2.4 million treatments of anti-flu drugs to 72 countries “most in need,” and France sent 100,000 doses worth $1.7 million to Mexico.

Associated Press writers Mark Stevenson, James Anderson and Katherine Corcoran contributed to this report.

By Juan Carlos Llorca, Lisa J. Adams

MEXICO CITY – Mexico began a cautious return to normal Tuesday, the government canceling Cinco de Mayo celebrations as traffic picked up in the capital and cafes reopened following a five-day shutdown to contain swine flu.

The canceled events included the largest one — a re-enactment of the May 5, 1862, victory over French troops in the central state of Puebla. And health experts warned that Mexico and the rest of the world needed to remain on guard against the virus.

Saying the outbreak is waning in Mexico, the epicenter of an illness that has sickened hundreds around the world, President Felipe Calderon announced it was nearly time to reopen businesses. Universities and high schools will open their doors Thursday, and younger schoolchildren are to report back to school May 11.

“The school schedule will resume with the guarantee that our educational institutions are in adequate hygienic condition,” Calderon said. He urged parents to join educators in a “collective” cleansing and inspection of schools nationwide.

“This is about going back to normalcy, but with everyone taking better care,” Calderon said.

Already more vehicles prowled the streets of the capital Monday than over the weekend, and fewer people wore surgical masks. Some cafes even reopened ahead of time.

Health Secretary Jose Cordova said infections were trending downward after Mexico’s 27 deaths, including a Mexican toddler who died in Texas. He said those infected appeared to pass the virus on to an average of 1.4 other people, near the normal flu rate of around 1.3.

Cordova said soccer stadiums and concert halls could reopen — but only if fans were kept 2 meters, about 6 1/2 feet, apart.

However, world health officials stressed that the global spread of swine flu was still in its early stages and a pandemic could be declared in the days to come. Experts inside Mexico’s swine flu crisis center warned that the virus remained active throughout Mexico and could bounce back once millions return to work and school.

“It’s clear that it’s just about everywhere in Mexico,” Marc-Alain Widdowson, a medical epidemiologist from the U.S. Centers for Disease Control and Prevention, told The Associated Press.

The World Health Organization said it was starting to ship 2.4 million treatments of antiflu drugs to the 72 countries “most in need” on Tuesday.

The agency declined to name the countries, but said they included Mexico, which has been hardest hit by the outbreak. Other countries included those that have been unable to afford building stockpiles of the drugs.

Scientists said the virus is spreading in the U.S. and that chances of severe cases could rise there as well, even as a New York City school reopened after the swine flu hit following a spring break trip by some students to Mexico.

“We are by no means out of the woods,” said Dr. Richard Besser, acting director of the CDC.

As of Monday, Mexico had 802 confirmed cases, and U.S. cases grew to at least 380 in 36 states. Globally, the virus had infected more than 1,447 people in 20 countries, according to the World Health Organization and other health bodies. South Korea, Italy and Germany all reported new cases Tuesday. Experts said the known cases were almost certainly only a fraction of the real total.

The latest figures from Mexico suggest the virus may be less lethal and infectious than originally feared. Only 38 percent of suspected cases have turned out to be swine flu, and no new deaths have been reported since April 29. But Cordova acknowledged that about 100 early deaths in which swine flu was suspected may never be confirmed because mucous or tissue samples were not collected.

WHO was studying whether to raise the pandemic alert to 6, its highest level, which would mean a global outbreak had begun. WHO uses the term pandemic to refer only to geographic spread and not to the severity of an illness. The two most recent pandemics — in 1957 and 1968 — were relatively mild.

“We do not know how long we will have until we move to Phase 6,” WHO Director-General Margaret Chan said. “We are not there yet. The criteria will be met when we see in another region outside North America, showing very clear evidence of community-level transmission.”

The Southern Hemisphere is particularly at risk. While Africa still hasn’t reported any swine flu infections and New Zealand is the only country south of the equator with confirmed cases, winter is only weeks away. Experts worry that typical winter flus could combine with swine flu, creating a new strain that is more contagious or dangerous.

“You have this risk of an additional virus that could essentially cause two outbreaks at once,” Dr. Jon Andrus said at the Pan American Health Organization’s headquarters in Washington.

Still, the U.N. health agency urged governments to avoid unproven actions to contain the disease, including group quarantines of travelers from Mexico and bans on pork imports.

China, Argentina and Cuba are among the nations banning regular flights to and from Mexico, marooning passengers at both ends. Mexico and China both sent chartered flights to each other’s countries to collect their citizens, with the chartered Mexican plane hopscotching China Tuesday to retrieve stranded residents. Argentina also chartered a flight to bring Argentines home.

In a televised message to the country late Monday, Calderon had harsh words for countries that he said are treating Mexicans unfairly. “Stop taking actions that only hurt Mexico and don’t contribute to avoid the transmission of the disease.”

Chinese authorities quarantined Mexicans and other passengers who came in close contact with them, even those who didn’t show symptoms.

China changed its visa rules for U.S. citizens. The Web site for the Chinese embassy and its consulates in the U.S said all visa applications would now require six business days to process, with express and rush services for visa applications suspended until further notice.

The new regulation, which became effective Monday, appears to apply to all Chinese visas, including tourist and business categories.

The American Embassy in Beijing said Tuesday that four U.S. citizens were quarantined in China. Embassy spokeswoman Susan Stevenson said two of the Americans were in Beijing and the other pair were in the southern province of Guangdong. She said two of them were released.

In Tokyo, 37 passengers and two flight attendants on a flight from Los Angeles were detained in a hotel after Japanese officials suspected one traveler of having swine flu. They were released about 10 hours later when the passenger, a Japanese woman coming back from Las Vegas, tested negative for swine flu, American Airlines spokesman Tim Smith said.

About 200 passengers who flew from the United Kingdom to Brunei were under quarantine in a Brunei hospital over swine flu fears Tuesday after three of them showed fever symptoms, an official said Tuesday.

MEXICO CITY – Mexican officials lowered their swine flu alert level in the capital on Monday and said they will allow cafes, museums and libraries to reopen this week, even as world health officials weighed raising their pandemic alert to the highest level.

Mexican officials declared the epidemic to be waning at its epicenter, announcing that Wednesday will conclude a five-day closure of nonessential businesses they credit for reducing the spread of the new virus. They haven’t decided when to reopen schools nationwide, saying inspections are necessary before students can return to class.

Global health officials urged countries to remain vigilant because the outbreak’s spread around the world remains in its early stages, but there were no imminent plans to raise the pandemic alert level.

Raising the alert level to 6, the highest, would mean that a global outbreak of swine flu is under way. WHO uses the term pandemic to refer to geographic spread rather than severity. Pandemics aren’t necessarily deadly. The past two pandemics — in 1957 and 1968 — were relatively mild.

“We do not know how long we will have until we move to Phase 6,” said Margaret Chan, head of the World Health Organization. “We are not there yet. The criteria will be met when we see in another region outside North America, showing very clear evidence of community-level transmission.”

WHO declares a level 5 alert when it believes a global outbreak is “imminent.” Though Mexican authorities believe the outbreak may have peaked there, WHO maintains it is still too early to tell if the outbreak is slowing down.

U.N. officials also emphasized that a pandemic alert is no justification for banning imports based on swine flu.

“Let me make a strong plea to countries to refrain from introducing measures that are economically and socially disruptive, yet have no scientific justification and bring no clear public health benefits,” Chan said. “Rational responses are always best — they are all the more important at a time of economic downturn.”

While Mexico began its first steps toward normalcy, the virus spread to Colombia in the first confirmed case in South America, where the coming winter means flu season is about to begin. More cases were confirmed in North America and Europe — including Portugal’s first. More than 1,000 people have been sickened worldwide, according to health and government officials.

But many questions remain about this virus — a new blend of genetic material from humans, birds and pigs — leading a number of countries to take urgent measures against arriving Mexicans or those who have recently traveled to Mexico.

In China, 71 Mexicans have been quarantined in hospitals and hotels, Foreign Secretary Patricia Espinoza said. Arriving Mexicans were taken into isolation, said Mexico’s ambassador, Jorge Guajardo. Even the Mexican consul in Guangzhou was briefly held after returning from a vacation in Cambodia.

And in Hong Kong, 350 people remained isolated in a hotel Monday after a Mexican traveler there was determined to have swine flu.

China’s Foreign Ministry denied it was discriminating against Mexicans. But Mexican President Felipe Calderon complained of the backlash, and sent a chartered plane to China Monday to pick up Mexican citizen wanting to return home.

“I think it’s unfair that because we have been honest and transparent with the world some countries and places are taking repressive and discriminatory measures because of ignorance and disinformation,” Calderon said.

Mexico also criticized Argentina, Peru and Cuba for banning flights. Argentina sent a chartered plan to Mexico to collect Argentines wanting to return home, and set up a field hospital at its airport in Buenos Aires to handle incoming passengers with symptoms.

WHO flu chief Keiji Fukuda said quarantines were a “long-established principle” that makes sense in the early phases of an infectious disease outbreak, but not once a full pandemic is under way.

“As we get later on into Phase 6 then these sorts of measures will become less useful because there will just be more infections around and you can’t quarantine everyone in the world,” he said.

A group of 25 Canadian university students and a professor also have been quarantined at a hotel in China since the weekend over swine flu fears. Canada has 103 confirmed cases of swine flu. The group does not have any flu symptoms, University of Montreal spokeswoman Sophie Langlois said Monday.

Mexico had 727 cases of swine flu and 26 deaths from the virus, Health Secretary Jose Angel Cordova said Monday.

The U.S. caseload grew to 245 confirmed cases in 35 states late Sunday, reflecting streamlined federal procedures and the results of tests by states, which have only recently begun confirming cases, said Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention.

The CDC’s acting chief, Dr. Richard Besser, said swine flu is spreading just as easily as regular winter flu.

“The good news is when we look at this virus right now, we’re not seeing some of the things in the virus that have been associated in the past with more severe flu,” Besser said. “That’s encouraging, but it doesn’t mean we’re out of the woods yet.”

In Alberta, Canada, officials quarantined about 220 pigs infected by a worker who recently returned from Mexico. It was the first documented case of the H1N1 virus being passed from a human to another species. Canada stressed that pigs often get the flu and there is no danger in eating pork.

Says measures against its citizens are ‘repressive’

A woman wearing a mask as a precaution against swine flu walks on the beach near the U.S.-Mexico border wall on Sunday in Tijuana, Mexico.

MEXICO CITY – Mexico chartered a plane on Monday to China to bring home 70 of its citizens who were seized at the airport and quarantined, declaring that the swine flu epidemic was no reason for “repressive and discriminatory measures.”

Mexican officials also declared the epidemic to be waning, but medical experts worldwide said it was to early to make that call.

While Mexico began its first tentative steps toward normalcy, weighing whether to reopen businesses and schools, the virus spread to Colombia in the first confirmed case in South America, where flu season is about to begin. A New York City school that had closed after dozens of students were infected with the virus reopened Monday.

More cases were confirmed in North America and Europe — including Portugal’s first — with the total number sickened worldwide rising to more than a 1,000 people, according to health and government officials.

But with the scope of the disease unknown, several countries have taken urgent measures against arriving Mexicans or those who have recently traveled to Mexico. In China, more than 70 Mexican travelers were quarantined in hospitals and hotels, and Mexicans on arriving flights were taken into isolation, said Mexico’s ambassador, Jorge Guajardo. Even the Mexican consul in Guangzhou was briefly held after returning from a vacation in Cambodia.

And in Hong Kong, 350 people remained isolated Monday in a hotel after a Mexican traveler there was determined to have swine flu.

One guest, Briton Mark Moore, complained that he had not shown symptoms and urged the government to lift the quarantine.

“The government is trying to show the world they are strong in organizing this,” the 37-year-old Singapore-based company director said in a phone interview. “I need to be in Singapore now. I have loads of things to do.”

Mexican President Felipe Calderon complained of the backlash against Mexicans abroad.

“I think it’s unfair that because we have been honest and transparent with the world some countries and places are taking repressive and discriminatory measures because of ignorance and disinformation,” Calderon said. “There are always people who are seizing on this pretext to assault Mexicans, even just verbally.”

The president did not single out any country. But the Foreign Relations Department said afterward that Mexico was sending a chartered jet Monday to bring back any citizens who wanted to leave China.

China’s Foreign Ministry denied it was discriminating against Mexicans.

But the Mexican Embassy in Beijing sent a circular out to all its citizens saying China had imposed “measures of unjustified isolation” in response to swine flu and urging trips there to be canceled or postponed.

“The imposition of measures which restrict freedom of movement such as quarantine and other forms of forced isolation by health authorities in other countries are not compatible” with norms on human rights, according to a document seen by The Associated Press.

The Mexican president said a nationwide shutdown and an aggressive information campaign appeared to have helped curtail the outbreak there.

“We have succeeded in detaining or at least slowing the spread of the virus precisely because the measures have been the correct ones,” Calderon said in an interview with state television broadcast Sunday night.

Mexico’s health chief said officials will decide Monday whether to reopen businesses and schools or extend the shutdown that has helped choke off the spread of swine flu but caused untold harm to the country’s economy.

The reopening “will not happen just like that,” Health Secretary Jose Angel Cordova said at a news conference. “There will have to be training, preparations for teachers and parents.”

Possible recommendations would be that there be a 2-meter (6.5-foot) distance kept between people in restaurants or theaters and that workers wear masks on the subway.

The World Health Organization said Mexico had 590 cases of swine flu and 25 deaths from the virus. Cordova said the last confirmed death was April 29 and the illness apparently peaked in Mexico between April 23 and April 28.

Health officials raised the number of confirmed U.S. swine flu cases to 245 in 35 states late Sunday. The new number reflects streamlining in federal procedures and the results of tests by states, which have only recently begun confirming cases, said Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention.

The CDC’s acting chief, Dr. Richard Besser, said swine flu is spreading just as easily as regular winter flu.

“The good news is when we look at this virus right now, we’re not seeing some of the things in the virus that have been associated in the past with more severe flu,” Besser said. “That’s encouraging, but it doesn’t mean we’re out of the woods yet.”

In Alberta, Canada, officials quarantined about 220 pigs infected by a worker who recently returned from Mexico. It was the first documented case of the H1N1 virus being passed from a human to another species. Canada stressed that pigs often get the flu and there is no danger in eating pork.

Cordova presented the most comprehensive description yet of the dead in Mexico.

He said 15 were female and seven were men. One possible explanation could be that women get poorer health care in Mexico because of its male-dominated culture, he said. Cordova also said only 4 percent were unemployed; the rest either had jobs or were housewives and students. More than 50 percent had not graduated from high school and only 11 percent had university education.

Pablo Kuri, an epidemiologist advising Cordova, told The Associated Press that tests have confirmed a swine flu death in Mexico City on April 11, two days earlier than what had been believed to be the first death.

Kuri also said there were no deaths among health care workers treating swine flu patients in Mexico, an indication that the virus may not be as contagious or virulent as initially feared.

MEXICO CITY – A top Mexican medical officer accused the World Health Organization of being slow to respond to the country’s warning about a health crisis that turned into a global swine flu scare. The WHO disputed the claim.

Hong Kong’s leader said Friday the territory has a confirmed case of swine flu, Asia’s first. Besides Mexico and the U.S., cases have also been confirmed in six European nations, Canada, New Zealand and Israel.

Mexico’s chief epidemiologist, Dr. Miguel Angel Lezana, told The Associated Press late Thursday his center alerted the Pan American Health Organization, a regional arm of WHO, on April 16 about an unusually late rash of flu and pneumonia cases in Mexico.

But he said no action was taken until eight days later, when the WHO announced it was worried the outbreak could become a pandemic.

“It seems it should have been more immediate,” Lezana, director of the National Epidemiology Center, told AP in a telephone interview. He called for an investigation into WHO’s handling of the crisis.

WHO officials said Friday the agency learned April 9 of cases of “suspicious influenza” from Mexico and responded quickly on April 24 when U.S. and Canadian laboratories identified the virus as a new strain of flu.

“We moved into operation within a matter of hours,” WHO spokesman Thomas Abraham told reporters.

Mexican health authorities came under criticism, particularly from frustrated citizens, for a slow and bumbling early response to the outbreak.

In the United States, the confirmed case count stood at 132. State lab operators say there are more cases than the confirmed number because they are not testing all suspected cases, focusing on finding new outbreak hot spots and limiting the flu’s spread.

In Mexico, the outbreak’s epicenter, new cases and the death rate were leveling off, the country’s top medical officer said. Health authorities said they have confirmed 300 swine flu cases and 12 deaths due to the virus.

“The fact that we have a stabilization in the daily numbers, even a drop, makes us optimistic,” Mexican Health Secretary Jose Angel Cordova said. “Because what we’d expect is geometric or exponential growth. And that hasn’t been the situation.”

The only confirmed swine flu death outside Mexico was a Mexican toddler who died in a Texas hospital Monday.

The United States is buying 13 million courses of anti-flu drugs to replenish its stockpile and sending 400,000 courses to Mexico. U.S. health officials say a swine flu vaccine could not be ready until fall at the earliest.

The Red Cross says it is readying an army of 60 million volunteers who could be deployed around the world to help slow the virus’ spread.

Mexico’s health secretary, Jose Angel Cordova, said Friday three more swine flu deaths were confirmed, bringing Mexico’s confirmed toll to 15. He said Mexico’s total sickened rose by 43, to 343.

Cordova said Mexicans with flu symptoms are now seeking medical attention quickly, and suspected swine flu cases are getting treatment even before the virus is confirmed, preventing deaths and limiting the virus’ spread.

“If the treatment is given the first day, the patient is practically not contagious,” Cordova said.

Cordova said outreach efforts to families of confirmed cases are turning up relatively few other cases.

Mexico shut down all but essential government services and private businesses Friday, the start of a five-day shutdown that includes a holiday weekend. Schools are also closed through Tuesday.

Mexico City’s notoriously clogged avenues were clear, crime was down and the smog dropped to levels normally seen only on holidays. Mexico is using the shutdown to determine whether to extend or ease emergency measures.

Lezana, the chief epidemiologist, said his department was alarmed by flu and pneumonia cases in Mexico earlier in April and notified the local office of PAHO by e-mail, following international protocol.

He said the illnesses raised a red flag because the flu was occurring at least a month after flu season normally ends in Mexico.

Four days later, PAHO still had not responded, so the National Epidemiology Center asked PAHO whether it needed more, Lezana said. He said PAHO responded the alert was being handled.

Lezana said that as far as he knew, the PAHO regional office in Washington and WHO took no action until April 24, when WHO announced an epidemic was under way.

Lezana had learned just the day before, from a testing of a sample that Mexico sent to a lab in Canada, that people were coming down with a new, mutated and lethal swine flu virus. By then, more than 1,000 people had been sickened in Mexico.

Daniel Epstein, a PAHO spokesman in Washington, told The Washington Post the agency received a message from Mexican authorities April 16 about an unusual outbreak. He described a system that sends messages to WHO headquarters in Geneva automatically.

WHO officials in Geneva confirmed Friday that the organization had received reports from Mexico of cases of suspicious influenza and that the organization reacted quickly when the new flu virus was identified on April 24.

WHO chief Dr. Margaret Chan was aboard a flight to the United States at the time but was briefed immediately when she landed, Abraham said. She canceled her appointments, met with U.S. and Mexican authorities and flew back to Geneva on April 25. That evening, WHO told the world it faced a possible flu pandemic.

“I think that is a pretty rapid response,” Abraham said.

WHO flu chief Dr. Keiji Fukuda, speaking before the Mexican epidemiologist issued his criticism, told reporters late Thursday there is always some delay when unusual illnesses are detected, particularly during flu season.

“Most diseases do not come out with people walking around with ‘new disease’ written on their forehead and ‘we need to call an international response,”‘ he said. “And in this case the countries which were affected earlier, they really were communicating in a very appropriate way.”

While Mexico waited for WHO to help, Lezana said, Mexican authorities tried to identify the outbreak and stop it. Mexican medical teams interviewed 472 people who may have come into contact with the first known swine flu fatality, a 39-year-old woman.

But only 18 of the 472, all hospital workers, were tested for swine flu. And in other parts of Mexico, health workers only this week started visiting the families of victims to find out whether they contracted it as well.

Associated Press writer Paul Haven contributed to this report.

CAIRO – Egypt’s government was hoping to look strong and proactive in the swine flu scare with its decision to slaughter all the country’s pigs, after taking heavy criticism at home for poor planning and corruption in past crises.

But instead, some Egyptians called the move a knee-jerk overreaction that even the World Health Organization said was unnecessary.

Egypt, which has no swine flu cases, is the only country in the world to order a mass pig slaughter in response to the disease. The move mirrored Egypt’s battle with bird flu, in which the government killed 25 million birds within weeks in 2006.

But international health officials said the swine flu virus that has caused worldwide fear is not transmitted by pigs, and that pig slaughters do nothing to stop its spread. The WHO on Thursday stopped using the term “swine flu” to avoid confusion.

In Egypt, even the editor of a pro-government newspaper criticized the order to slaughter the estimated 300,000 pigs, which was pushed by parliament and issued by the government.

“Killing (pigs) is not a solution, otherwise, we should kill the people, because the virus spreads through them,” wrote Abdullah Kamal of the daily Rose El-Youssef. “The terrified members of parliament should have concentrated on asking the government first about the preventive measures and ways of confronting the problem.”

The Egyptian government has come under criticism in past years for being caught flat-footed by crises.

A rockslide that crushed a Cairo neighborhood and killed at least 100, and a series of fires — including one that burned down the upper house of parliament — highlighted how ill-prepared emergency services are. A 2005 ferry sinking that killed 1,000 raised an uproar over poor safety conditions.

Many accused the government of not taking precautions when bird flu first appeared in Asia in 2003. When the first case appeared in Egypt in 2006, the government carried out mass bird culls, but the disease has killed more than two dozen people since.

With the new flu scare, the government “took a precautionary step because they were afraid there would be a case here, and then they would face questions about why they didn’t take this step,” said Nader Noureddin, an agricultural resources expert at Cairo University’s Agricultural College.

The government likely felt confident slaughtering pigs would not spark any public backlash in predominantly Muslim Egypt, where the majority of the population does not eat pork. Pig raising and consumption is limited to the country’s Christian minority, estimated at 10 percent of the population.

Still, the opposition Muslim Brotherhood was critical of the slaughter on the grounds it was not thought out.

“The problem is that the government here deals with things in emotional ways,” said Essam el-Erian, a top Brotherhood leader. “It acts with the memory of what happened during the bird flu crisis.”

The government initially said it would not provide compensation for slaughtered pigs since the meat could be sold. But now it is proposing paying farmers $180 for each pig — a step that would cost the government an estimated $54 million.

Coptic Christian leaders — including the Coptic pope — condoned the slaughter, and two Coptic lawmakers were among the most vocal supporters, likely to ensure that the Christian community is not blamed if a case does ever arise in Egypt.

But pig farmers — overwhelmingly Christian — were angered. Government efforts to start the slaughter Wednesday were met with farmers who hurled stones at Health Ministry trucks.

“This is the livelihood of a segment of the people,” said Youssef Sidhom, an editor of the Al-Watani newspaper and prominent Coptic figure. “You can’t just do something on the national level and ignore a segment of the population.”

300 schools closed; vaccine won’t be ready until fall

Teresa Long, a nurse practitioner at Take Care Clinic in Wilmington, Del., conducts tests on Paul Johnson, who came in with flulike symptoms. Johnson tested positive for strep.

WASHINGTON – U.S. authorities are pledging to eventually produce enough swine flu vaccine for everyone but the shots couldn’t begin until fall at the earliest.

Worries about the spread of the virus mounted Thursday as the nation’s swine flu caseload passed 100, and nearly 300 schools closed in communities across the country. Federal officials had to spend much of the day reassuring the public it’s still safe to fly and ride public transportation after Vice President Joe Biden said he wouldn’t recommend it to his family.

“There’s not an increased risk there,” Dr. Richard Besser, acting director of the Centers for Disease Control and Prevention, said Friday. “If you have the flu or flu-like symptoms, you shouldn’t be getting on an airplane or you shouldn’t be getting in the subway, but for the general population that’s quite fine to do.”

Clinics and hospital emergency rooms in New York, California and some other states are seeing a surge in patients with coughs and sneezes that might have been ignored before the outbreak.

Scientists were racing to prepare the key ingredient to make a vaccine against the never-before-seen flu strain — if it’s ultimately needed. But it will take several months before the first pilot lots begin required human testing to ensure the vaccine is safe and effective. If all goes well, broader production could start in the fall.

“We think 600 million doses is achievable in a six-month time frame” from that fall start, Health and Human Services Assistant Secretary Craig Vanderwagen told lawmakers.

“I don’t want anybody to have false expectations. The science is challenging here,” Vanderwagen told reporters. “Production can be done, robust production capacity is there. It’s a question of can we get the science worked on the specifics of this vaccine.”

Until a vaccine is ready, the government has stockpiled anti-viral medications that can ease flu symptoms or help prevent infection. The medicines are proving effective.

Reassurances from top health officials didn’t stop the questions from coming.

An estimated 12,000 people logged onto a Webcast where the government’s top emergency officials sought to cut confusion by answering questions straight from the public: Can a factory worker handling parts from Mexico catch the virus? No. Can pets get it? No.

And is washing hands or using those alcohol-based hand gels best? Washing well enough is the real issue, Besser said. He keeps hand gel in his pocket for between-washings but also suggested that people sing “Happy Birthday” as they wash their hands to make sure they’ve washed long enough to get rid of germs.

Although it is safe to fly, anyone with flu-like symptoms shouldn’t be traveling anywhere, unless they need to seek medical care.

Continental Airlines Inc. said Friday that it will temporarily cut the number of U.S. departures to Mexico and use smaller planes as fewer passengers book flights there. Many travelers have become increasingly concerned about going to Mexico because of the recent swine flu outbreak. There are 300 confirmed cases in Mexico and 12 dead, health authorities said Thursday.

“We were already experiencing soft market conditions due to the economy, and now our Mexico routes in particular have extra weakness,” Chairman and Chief Executive Larry Kellner said in a statement.

The swine flu outbreak penetrated over a dozen states and even touched the White House, which disclosed that an aide to Energy Secretary Steven Chu apparently got sick helping arrange President Barack Obama’s recent trip to Mexico but that the aide did not fly on Air Force One and never posed a risk to the president.

The Washington Post identified the aide as Marc Griswold, a former Secret Service agent who was doing advance work for Chu. It said that Griswold has complained about the infection placing his family in an awkward position with family and neighbors.

“We’re not the Typhoid Mary family, for goodness sake,” he said. “We’ve been told that we’re not contagious. We’re already past the seven-day mark for that.”

So far U.S. cases are mostly fairly mild with one death, a Mexican toddler who visited Texas with his family — unlike in Mexico where more than 160 suspected deaths have been reported. Most of the U.S. cases so far haven’t needed a doctor’s care, officials said.

Still, the U.S. is taking extraordinary precautions — including shipping millions of doses of anti-flu drugs to states in case they’re needed. The World Health Organization is warning of an imminent pandemic because scientists cannot predict what a brand-new virus might do. A key concern is whether this spring outbreak will surge again in the fall.

The CDC confirmed 109 cases Thursday, and state officials confirm 22 more. Cases now are confirmed in New York, Texas, California, South Carolina, Kansas, Massachusetts, Indiana, Ohio, Arizona, Michigan, Nevada, New Jersey, Delaware, Maine, Colorado, Georgia and Minnesota.

Besser appeared Friday morning on ABC’s “Good Morning America” and NBC’s “Today” show.

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LATEST DEVELOPMENTS

• The World Health Organization increases its tally of confirmed swine flu cases around the world to 331.

• In U.S., CDC confirms 109 cases and state officials confirm 23 more. CDC confirms: 50 in New York; 26 in Texas; 14 in California; 10 in South Carolina; two each in Kansas and Massachusetts; and one each in Indiana, Ohio, Arizona, Michigan and Nevada. State officials confirm five in New Jersey; four in Delaware; three additional cases in Arizona; four additional cases in California; two each in Colorado and Virginia; one additional case in Michigan; and one each in Georgia and Minnesota.

• The World Health Organization says it will stop using the term “swine flu” to avoid confusion over the danger posed by pigs. It will instead refer to the virus by its scientific name, “H1N1 influenza A.”

The Associated Press

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ON THE WEB

Health and Human Services Department swine flu site: www.pandemicflu.gov