The global outbreak appears mild, but skittishness is evident. Not long after Switzerland lifted its advisory against travel to Mexico and the United States on Tuesday, the Japanese national women's soccer team canceled a tour to North America, where most swine flu cases have been reported.

In Mexico's Baja California state, on the U.S. border, 5,689 children were turned away from schools when classes resumed Monday because they had symptoms like runny noses, headaches or sore throats, the state education department reported Tuesday.

Three more nations — Cuba, Thailand and Finland — reported their first confirmed swine flu cases, all in people who had traveled to Mexico. A 24-year-old Hong Kong man returning from the United States was confirmed Wednesday as the Chinese territory's second case of swine flu, authorities said.

And China confirmed its second case of swine flu on the mainland, in a man who had recently returned from Canada.

There are now 33 countries reporting an estimated total of 5,916 confirmed swine flu cases, including 3,009 in 45 U.S. states, 2,282 in Mexico and 358 in Canada.

The death total is relatively low — 63, of which 58 were in Mexico, three in the U.S., one in Canada and one in Costa Rica.

But health experts worry about the chance that the virus might become more lethal in the coming months, saying it is important not to overuse antiviral drugs since supplies are limited.

The World Health Organization said Tuesday that antiviral drugs should be given to only patients most at risk.

Its comments appeared aimed at European countries, which have been using antiviral drugs such as Tamiflu and Relenza much more aggressively than the U.S. and Mexico, administering them whenever possible in an attempt to contain the virus before it spreads more widely.

Officials from EU and Latin American nations, including Mexico, were meeting in Prague on Wednesday to discuss ways of combating the threat.

A WHO medical expert, Dr. Nikki Shindo, said the U.N. agency thinks antivirals should be targeted mainly at people already suffering from other diseases or complications — such as pregnancy — that can lower a body's defenses against flu.

The U.S. Centers for Disease Control and Prevention also said pregnant women in particular should take the drugs if they are diagnosed with swine flu — even though the effects on the fetus are not completely known.

Pregnant women are more likely to suffer pneumonia when they catch flu, and flu infections have raised the risk of premature birth in past flu epidemics. A pregnant Texas woman who had swine flu died last week, and at least 20 other pregnant women have swine flu, including some with severe complications.

For all these reasons, risks from the virus are greater than the unknown risks to the fetus from Tamiflu and Relenza, said Dr. Anne Schuchat of the CDC.

"We really want to get the word out about the likely benefits of prompt antiviral treatment" for pregnant women, she said.

Shindo, at WHO, said each country's health experts must decide if infected people should immediately be treated with antivirals — a decision that also must take into account how many antivirals are available.

"As part of pandemic preparedness plans, we urge countries to plan for prioritization," Shindo said.

Swiss pharmaceuticals company Roche Holding AG announced it was donating enough Tamiflu for 5.65 million more people to WHO. A further 650,000 packets containing smaller doses of the drug will be used to create a new stockpile for children.

Mexican authorities had enough Tamiflu for 1 million people at the start of the outbreak and have received more, building reserves of 1.5 million courses.

Mexico is giving Tamiflu to anyone who has had direct contact with a person infected with swine flu, Health Secretary Jose Angel Cordova said. And now that schools are back in session, authorities plan to give Tamiflu to any children who show symptoms and are suspected of being infected.

CDC officials said that while the swine flu may seem mild now, there is a danger the virus will mutate into something more dangerous — perhaps by combining with the more deadly but less easily spread bird flu virus circulating in Asia and Africa.

Another concern is that it will combine with the northern winter's seasonal H1N1 virus. While not unusually virulent, it was resistant to Tamiflu, and health officials worry it could make the new swine flu resistant to Tamiflu as well.

Cordova said the worst appears over in Mexico. He said the two swine flu deaths reported Tuesday, along with additional confirmed cases, was a result of a backlog in testing. The last confirmed infection occurred Friday, he said.

Mexico is now working to revive its economy from the ill effects of the epidemic.

Incoming airliners have been virtually empty of tourists, pummeling the country's third-largest source of legal foreign income, and some countries have banned imports of Mexican pork even though health experts say people can't catch swine flu from meat.

Mexico's economy secretary, Gerardo Ruiz, said Tuesday that Ecuador, Honduras, the United Arab Emirates and Kazakhstan agreed to lift their bans on Mexican pork, after Mexico protested. He said Mexico was using similar persuasion seeking to end restrictions still imposed by at least four other nations.