The new swine flu is rattling Americans from coast to coast and President Barack Obama pledged "to do whatever it takes" to battle an emergency that world health authorities warned is inching closer to a full-fledged pandemic.

"This is obviously a very serious situation, and every American should know that their entire government is taking the utmost precautions and preparations," Obama declared, just hours after the World Health Organization pointed to spreading U.S. infections as it ramped up its grim warnings.

But with nearly 100 confirmed cases in 11 states and many more suspected, Obama also stressed that average people have some power to fend off this new flu just like they can guard against the garden-variety kind.

"It sounds trivial but it makes a huge difference," Obama said at a news conference Wednesday night on his 100th day in office. He repeatedly urged people to wash their hands, cover their coughs and stay home rather than spread germs when they're feeling sick.

Dr. Richard Besser, acting chief of the Centers for Disease Control and Prevention, said in Atlanta on Wednesday there were confirmed cases in 10 states, including 51 in New York, 16 in Texas and 14 in California. The CDC counted scattered cases in Kansas, Massachusetts, Michigan, Arizona, Indiana, Nevada and Ohio. State officials in Maine said laboratory tests had confirmed three cases in that state, not yet included in the CDC count.

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Scores of schools were closed around the country and more might need to be shut down temporarily, triggering a chain reaction as parents left without child care can't report to work. Homeland Security Secretary Janet Napolitano urged U.S. businesses to figure out who can telecommute and to take other steps to keep operations going for what promises to be a long period of uncertainty.

"We're going to be working through this for a while," Napolitano said.

But barely a week after the virus' discovery, the outbreak already has cash-strapped states feeling pinched. In Kansas, with two confirmed cases, the health secretary said he'd need more money to keep the state laboratory and other offices working to identify and control the swine flu. Obama has requested an additional $1.5 billion to assist with the outbreak.

Of particular concern is New York City's outbreak, with 51 confirmed cases and tests under way on three probable ones outside the city. City Health Commissioner Thomas Frieden said Wednesday that all those with confirmed cases are recovering, but two more city schools closed because of suspected cases — in addition to a Queens Catholic school with a large outbreak.

Schools aren't the only focus. In California, dozens of Marines were under quarantine to see if they'll develop illness after contact with a comrade confirmed to have the new flu.

Mexico, hardest-hit with 168 suspected deaths, reported that new cases and mortality finally may be leveling off thanks to aggressive public health measures. But the World Health Organization, particularly worried about patterns of illness in the U.S., raised its alert level to its second-highest notch and called for intensified efforts to produce a vaccine against infections now seen on four continents.

U.S. scientists are racing to develop the key vaccine ingredient — a strain of the virus engineered to trigger the immune system. But they cautioned Wednesday that it would take several months before enough doses could roll off assembly lines for the necessary testing in human volunteers to see if a swine flu vaccine is safe and effective.

"It's going now as fast as it can go," Dr. Bruce Gellin, head of the National Vaccine Program Office, said of the work. "We're hopeful that by early fall we could potentially have something available."

The U.S. has reported the only death outside Mexico — a Mexican toddler who visited Texas with his family — and much milder illnesses than south of the border, a difference that health authorities can't yet explain. Regardless, Obama resisted calls to close the U.S. border as "akin to closing the barn door after the horses are out."

Emergency Response

There is no vaccine to prevent infection but U.S. health officials aim to have a key ingredient for one ready in early May, the big step that vaccine manufacturers are awaiting. But even if the World Health Organization ordered up emergency vaccine supplies — and that decision hasn't been made yet — it would take at least two more months to produce the initial shots needed for human safety testing.

"We're working together at 100 miles an hour to get material that will be useful," Dr. Jesse Goodman, who oversees the Food and Drug Administration's swine flu work, told The Associated Press.

Obama asked Congress for $1.5 billion in emergency funds to help build more drug stockpiles and monitor future cases, as well as help international efforts to avoid a full-fledged pandemic.

In Washington, Homeland Security Secretary Janet Napolitano was questioned closely by senators about whether the U.S. should close its border with Mexico, repeated the administration's position that questioning of people at borders and ports of entry was sufficient for now and said closing borders "has not been merited by the facts."

In a bit of good news, Mexico's health secretary, Jose Cordova, late Tuesday called the death toll there "more or less stable."

Swine Flu vs. Seasonal Influenza

“The illness is consistent with seasonal influenza and has generally the same symptoms of seasonal influenza,” Fukuda said. “Our information to date shows that the infection can range from very mild, requiring no hospitalization and recovering after a few days, to fatal, which is also in keeping with seasonal influenza."

Fukuda said there is no evidence that the virus is spreading from pigs or that it is unsafe to eat pork.

Authorities sought to keep the crisis in context: Flu deaths are common around the world. In the U.S. alone, the CDC says about 36,000 people a year die of flu-related causes.

Children, especially those younger than age 5, are particularly vulnerable to flu and its complications, and every year children die from seasonal flu.

According to the CDC, more than 20,000 children younger than age 5 are hospitalized every year because of seasonal flu. In the 2007-08 flu season, the CDC received reports that 86 children nationwide died from flu complications.

As of April 11, CDC had received reports of 53 seasonal flu-related deaths in children during the current seasonal flu season.

Still, the CDC calls the new strain a combination of pig, bird and human viruses for which people may have limited natural immunity.

Hence the need for a vaccine. Using samples of the flu taken from people who fell ill in Mexico and the U.S., scientists are engineering a strain that could trigger the immune system without causing illness. The hope is to get that ingredient — called a "reference strain" in vaccine jargon — to manufacturers around the second week of May, so they can begin their own laborious production work, said CDC's Dr. Ruben Donis, who is leading that effort.

The first doses of a swine-flu vaccine could be available about 15 weeks after the World Health Organization decides what kind of vaccine it wants companies to produce, Sanofi-Aventis SA's chief executive said in an interview with the Wall Street Journal.

The Associated Press contributed to this report.

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Swine Flu Timeline

Swine Flu Q & A

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