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Wearing face masks to protect against infection, Jaqueline Garcia Gonzalez, right, and Alan Martinez wait in line Thursday to be examined at a mobile medical brigade in Mexico City

WASHINGTON — Nearly 300 schools around the country closed as the nation's swine flu caseload reached at least 130 Thursday. U.S. authorities said they eventually could produce enough vaccine for everyone if necessary – but the shots couldn't begin until fall at the earliest.

The outbreak penetrated more than 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 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.

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, answered Dr. Richard Besser, acting chief of the federal Centers for Disease Control and Prevention. 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.

It is safe to fly, U.S. officials found themselves stressing after Vice President Joe Biden got off message Thursday. Biden said he'd discourage family members from flying or even taking the subway. The White House insisted the vice president meant to say he was discouraging just nonessential travel to Mexico, the hardest-hit area.

"It is safe to fly. There is no reason to cancel flights," Transportation Secretary Ray LaHood said. Not just planes but "all modes of transportation are safe in America," he said.

But anyone with flu-like symptoms shouldn't be traveling anywhere unless they need to seek medical care – the same advice that doctors give during the winter when regular flu kills 36,000 Americans each year.

"If you're ill, you shouldn't get on an airplane or any public transport to travel," CDC's Dr. Anne Schuchat told a congressional hearing. "If you're sick, stay home. I can't tell you how many times I've said that this week."

So far, U.S. cases are fairly mild for the most part, with one death, a Mexican toddler who visited Texas with his family. In Mexico, more than 160 suspected deaths have been reported. In fact, Schuchat said most of the U.S. cases so far didn't need a doctor's care.

The World Health Organization said the number of confirmed H1N1 flu cases worldwide reported to WHO jumped overnight from 148 to 236.

Dr. Keiji Fukuda, a WHO assistant director-general, said the biggest part of that increase was from Mexico – with confirmed cases there rising from 26 to 97 – and resulted primarily from laboratory workers making their way through the backlog of stored specimens, not from new cases.

To date, he said, only seven of the 176 influenza-related deaths in Mexico have been confirmed to be H1N1 flu. Mexican authorities said the number of deaths confirmed to be linked to H1N1 is 12.

Mexican Health Secretary Jose Angel Cordova told The Associated Press that new cases have leveled off and the death rate has been nearly flat for several days. He said the next few days would be critical in determining whether the virus was truly on the decline.

"The fact that we have a stabilization in the daily numbers, even a drop, makes us optimistic," he said. "Because what we'd expect is geometric or exponential growth. And that hasn't been the situation. So we think we're on the right track."

Mexico has imposed what amounts to a five-day shutdown of the country, beginning today, in hopes of slowing the virus. All but the most essential government services will be suspended, most businesses have been urged to close, and Mexicans have been encouraged to stay in their homes.

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