WASHINGTON – 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.

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."

MEXICO CITY – Mexico readied a "temporarily closed" sign — taking the drastic step of ordering a suspension of nonessential federal government and private business activity as it tried to squelch a swine flu epidemic. The World Health Organization ratcheted up an alert and warned that "all of humanity" is threatened.

The dire warning showed that world health officials are very worried about the potential for massive numbers of deaths worldwide from the mutated virus, even though the epidemic so far has claimed only a confirmed eight lives in Mexico and one in the United States. Roughly 170 deaths are suspected of having been caused by the virus in Mexico.

The Phase 5 alert, indicating a pandemic could be imminent as the virus spread further in Europe, prompted Mexico to announce the partial May 1-5 shutdown, Mexican Health Secretary Jose Cordova said late Wednesday.

In Washington, President Barack Obama promised "great vigilance" in confronting the outbreak which has sickened nearly 100 people in 11 states and forced schools to close. A Mexican toddler who visited Texas with his family died Monday night in Houston, becoming the first fatality in the U.S., and 39 Marines were confined to their base in California after one came down with the disease.

The virus, a mix of pig, bird and human genes to which people have limited natural immunity, has also spread to Canada, New Zealand, Britain, Germany, Spain, Israel and Austria.

"It really is all of humanity that is under threat during a pandemic," WHO Director General Margaret Chan said in Geneva. "We do not have all the answers right now, but we will get them."

In a televised address, Mexican President Felipe Calderon praised "the heroic work" of doctors and nurses and asked his countrymen to literally stay in their homes between May 1 and May 5, saying "there is no safer place to protect yourself against catching swine flu, than in your house."

"In recent days, Mexico has faced one of the most serious problems in recent years," Calderon said Wednesday night. He brushed aside criticisms that his government's response was slow, stressing several times that authorities had reacted "immediately."

School in Mexico has already been canceled until May 6. During the shutdown, essential services like transport, supermarkets, trash collection and hospitals will remain open.

Calderon said authorities would use the partial shutdown to weigh whether to extend the emergency measures, or "if it is possible to phase out some" restrictions.

The outbreak appeared to already be stabilizing in Mexico, the epicenter. Confirmed swine flu cases doubled Wednesday to 99, but new deaths finally seemed to be leveling off after an aggressive public health campaign was launched when the epidemic was declared April 23. Although 17 new suspected deaths were reported, only one additional confirmed death was announced Wednesday night, for a total of eight countrywide. The virus is believed to have sickened as many as 2,955 people across the country, though hospital records suggest the outbreak may have peaked here last week.

The WHO said the global threat is nevertheless serious enough to ramp up efforts to produce a vaccine against the virus. It declared a Phase 5 outbreak — the second-highest on its threat scale — for the first time ever, indicating a pandemic could be imminent.

In the U.S., eight states closed schools Wednesday, affecting 53,000 students in Texas alone.

Obama said his administration has made sure that needed medical supplies are on hand and he praised the Bush administration for stockpiling 50 million doses of antiviral medications.

"The key now is to just make sure we are maintaining great vigilance, that everybody responds appropriately when cases do come up. And individual families start taking very sensible precautions that can make a huge difference," he said.

Ecuador joined Cuba and Argentina in banning travel to or from Mexico and Peru banned flights from Mexico. The Panama Canal Authority ordered pilots and other employees who board ships passing through the waterway to use surgical masks and gloves. An average of 36 ships per day use the canal, most from the United States, China, Chile and Japan.

In France, President Nicolas Sarkozy met with Cabinet ministers to discuss swine flu, and the health minister said France would ask the European Union to suspend flights to Mexico.

The U.S., the European Union and other countries have discouraged nonessential travel to Mexico. Some countries have urged their citizens to avoid the United States and Canada as well. Health officials said such bans would do little to stop the virus.

Medical detectives have not pinpointed where the outbreak began. Scientists believe that somewhere in the world, months or even a year ago, a pig virus jumped to a human and mutated, and has been spreading between humans ever since.

China has gone on a rhetorical offensive to squash any suggestion it's the source of the swine flu after some Mexican officials were quoted in media reports in the past week saying the virus came from Asia and the governor of Mexico's Veracruz state was quoted as saying the virus specifically came from China.

One of the deaths in Mexico directly attributed to swine flu was that of a Bangladeshi immigrant, said Mexico's chief epidemiologist Miguel Angel Lezana.

Lezana said the unnamed Bangladeshi had lived in Mexico for six months and was recently visited by a brother who arrived from Bangladesh or Pakistan and was reportedly ill. The brother has left Mexico and his whereabouts are unknown, Lezana said. He suggested the brother could have brought the virus from Pakistan or Bangladesh.

By March 9, the first symptoms were showing up in the Mexican state of Veracruz, where pig farming is a key industry in mountain hamlets and where small clinics provide the only health care.

The earliest confirmed case was there: a 5-year-old boy who was one of hundreds of people in the town of La Gloria whose flu symptoms left them struggling to breathe.

Days later, a door-to-door tax inspector was hospitalized with acute respiratory problems in the neighboring state of Oaxaca, infecting 16 hospital workers before she became Mexico's first confirmed death.

Neighbors of the inspector, Maria Adela Gutierrez, said Wednesday that she fell ill after pairing up with a temporary worker from Veracruz who seemed to have a very bad cold. Other people from La Gloria kept going to jobs in Mexico City despite their illnesses, and could have infected people in the capital.

Cordova, the Mexican health secretary, said getting proper treatment within 48 hours of falling ill "is fundamental for getting the best results" and suggested the virus can be beaten if caught quickly and treated properly. But it was neither caught quickly nor treated properly in the early days in Mexico, which lacked the capacity to identify the virus, and whose health care system has become the target of widespread anger and distrust.

In case after case, patients have complained of being misdiagnosed, turned away by doctors and denied access to drugs. Monica Gonzalez said her husband, Alejandro, already had a bad cough when he returned to Mexico City from Veracruz two weeks ago and soon developed a fever and swollen tonsils.

As the 32-year-old truck driver's symptoms worsened, she took him to a series of doctors and finally a large hospital. By then, he had a temperature of 102 and could barely stand.

"They sent him away because they said it was just tonsillitis," she said. "That hospital is garbage."

Gonzalez finally took her husband to Mexico City's main respiratory hospital, "dying in the taxi." Doctors diagnosed pneumonia, but it may be too late: He has suffered a collapsed lung and is unconscious. Doctors doubt he will survive.

Swine flu has symptoms nearly identical to regular flu — fever, cough and sore throat — and spreads like regular flu, through tiny particles in the air, when people cough or sneeze. People with flu symptoms are advised to stay at home, wash their hands and cover their sneezes.

NEW YORK – Dr. Ed Craig figured when called upon by MSNBC for studio commentary on swine flu Wednesday that his job was to calm people down.

Craig, a professor of clinical surgery at Cornell Medical School, found it wasn't really necessary. As the story of the epidemic spread rapidly over the past few days, the coverage may be most notable for the caution displayed by media outlets who most often throw it to the wind.

"I've been very impressed by the recognition from the beginning that we had a real responsibility here to keep things in perspective," said Rome Hartman, executive producer of "BBC World News America." "We got an e-mail last weekend saying let's make sure we're paying attention to this story and covering it as competitively as we can but also understand the responsibility not to be hyperbolic. I know every news organization has been having that conversation."

It's a given now that every big story is overblown by the 24-hour cable news networks because of all the time they need to fill and a short attention span.

Yet swine flu has yet to dominate the airwaves that way. Coverage of President Barack Obama's 100-day marker and the party affiliation switch of Sen. Arlen Specter has taken as much time. There's been the usual number of "breaking news" or "news alert" graphics, but CNN has quietly phased out an alarmist graphic showing a man in a face mask.

"While the volume (of stories) would suggest we are in some kind of pandemic, the tone of the content has been calmer than that," said Tom Rosenstiel, director of the Project for Excellence in Journalism.

Craig suggested that was due in part to the response of federal health authorities, who have frequently made themselves available for news conferences.

"I think they have been responsible and upfront," he said, "and I think it probably reflects this administration's early attempts to let people know what they know and to say it if they don't know the answer."

Many newspaper headlines stopped short of screaming: "Relax, Don't Panic," urged the front of the Casper Star-Tribune in Wyoming. "Michiganders, Don't Panic Over Swine Flu Yet," urged the Detroit Free Press. "People Urged Not to Panic Over Flu," said the Tulsa (Okla.) World.

The Columbus Dispatch in Ohio hedged its bets: "Fear? Or Fear Not?"

It's never unanimous, of course. The New York Daily News headlined: "Flu spreading like wildfire through the city." The newspaper sent a reporter walking through the city in a face mask to gauge reaction, and he was stopped by a British TV crew wanting to film him. A newspaper reporter interviewing passengers coming off a plane from Mexico in the Newark, N.J., airport wore rubber gloves.

A television station in Orlando caused a stir by reporting that a Mexican tourist visiting Walt Disney World was Florida's first swine flu victim. The state called a news conference to refute the report.

When editors at the San Antonio (Tex.) Express-News learned last week of the city's first two confirmed swine flu cases, they debated even putting it into the paper. They decided to run a short story that ran on the back of the local news section, said Jamie Stockwell, deputy metro editor.

The story has exploded in all directions since then, but editors are being careful to keep things in perspective, she said.

"We've lived through 9/11," Stockwell said. "We've lived through anthrax scares. We've lived through the threat of terrorists and through mass shootings on campuses. To add to the collective fear of our residents of perhaps a virus or illness that could kill them, that would be completely irresponsible to press it that far."

The San Diego Union Tribune has 18 reporters working on the story. "It's sort of like we're in the midst of covering a wildfire," said Laura Wingard, metro editor. "There's so much going on."

Yet editors there had long debates about alarming people before it first put the story in the front page, she said. Wingard said she makes sure every day to include in the paper the number of people who die each year from traditional flu, to make sure readers aren't overly worried about this threat.

"We're saturating people with information," she said, "and I wonder when it does become white noise."

The epidemic got its most prominent public face — a cute one, at that — when Mexican health officials identified 5-year-old Edgar Hernandez of La Gloria, Mexico as the earliest known swine flu victim. CNN's Sanjay Gupta traveled with a crew to meet him at a home that is surrounded by pig farms.

Hernandez may never know the extent to which his picture traveled the world. The Toronto Globe and Mail wrote about "The boy at swine flu's ground zero" and the Sydney (Australia) Morning Herald told about him in a story headlined "Unravellng the history of a mystery virus."

The story was front page news all over the world. The Japan Times published a front-page picture of men wearing face masks in a Chinese airport. South Korea's Segye Times ran a large picture of a Mexican street filled with people in face masks. A supportingly large picture of a man from Mexico in a decorated mask dominated the front page of The Times in Johannesburg, South Africa.

In New York, the Daily News found a 17-year-old swine flu victim who described how sick she was in the most modern of terms.

"I couldn't text," said high school senior Sophia Goumokas.