President Obama said today that while the United States is still preparing for the worst in the wake of the swine flu scare, the outbreak could end up falling short of a pandemic and run its course just "like ordinary flus" that pass through the country every winter.
"I'm optimistic that we're going to be able to manage this effectively," Obama said.
"We don't know for certain that this will end up being more severe than other flus," he said. "It may turn out that H1N1 runs its course like ordinary flus."
The head of the CDC's influenza division, Dr. Nancy Cox, said today that preliminary research suggests the makeup of this current virus is lacking some key components of the 1918 flu pandemic that killed between 30 million and 50 million people and to which the new strain has recently been compared.
"What we have found by looking very carefully at the sequence of the new H1N1 virus is that we're not seeing the markers for virulence that we saw in the 1918 virus," she said. But she added that scientists still may not know all they need to know about the 1918 H1N1 strain and are "continuing to look for virulence markers."
Dr. Julie Gerberding, former head of the CDC, said on ABC's "Good Morning America" that we "have to be careful not to over-rely on that kind of information because these flu viruses always evolve."
Officials still remain cautious about the outbreak. Friday afternoon a United Airlines flight from Germany to Washington, D.C., was diverted to Boston after a passenger complained of flu-like symptoms.
Meanwhile, as more schools across the United States close in response to the swine flu outbreak, some estimate that more than a quarter of a million schoolchildren were out of school this morning.
In Brownsville, Texas, officials ordered the closing of the entire school district today, a move taken in several school districts around the country, including nearby Fort Worth.
But Dr. Richard Besser, acting director of the Centers for Disease Control and Prevention, told "GMA" they still believe schools should only be closed if they have a confirmed case of the flu.
"Our recommendation right now is you have a case in the school, you dismiss the students until you've been able to sort out the situation and ensure there is not ongoing transmission."
The school closures have turned the lives of thousands of families upside down as they struggle to arrange child care and work schedules.
But Besser said the final decision should still be made locally, in accordance with the communities' "comfort level."
In the U.S., the CDC reports a total of 144 cases in 21 states and one confirmed death, with more flu cases likely to come as state and federal health officials analyze samples.
The latest state to join the list of state-confirmed cases as of this afternoon is Florida, where Gov. Charlie Crist announced two cases of swine flu -- an 11-year-old boy and a 17-year-old girl.
South Korea and Germany became the latest countries to report confirmed cases of swine flu Friday. A total of 12 countries now have at least one case, and the number of confirmed cases is 331, according to the World Health Organization, up from 257 Thursday.
U.S. authorities have promised to produce enough swine flu vaccine for the country, but it won't be available until fall at the earliest.
U.S. Health and Human Services Assistant Secretary Craig Vanderwagen told lawmakers that it would take several months before pilot tests on humans could ensure that any vaccine would be safe and effective against the flu. Assuming that everything goes well, mass production of the vaccine could begin in the fall.
"We think 600 million doses is achievable in a six-month time frame" from that fall start, he said, adding, "I don't want anybody to have false expectations. The science is challenging here."
Until then, the government has stockpiled anti-viral medicines to help ease symptoms of the flu and prevent further infection. So far, the medications are said to have worked effectively.
In the midst of concerns that the current outbreak could resurface as a new flu strain in the fall, U.S. authorities are now shipping millions of doses of anti-flu drugs to all states.
"We don't know whether we're going to need those or not, but we wanted to be ready," said Dr. Anne Schuchat of the Centers for Disease Control.
As the flu spreads, stress levels have soared nationwide. U.S. prescriptions for anti-viral flu medications spiked this week, increasing almost 900 percent, according to prescription tracker SDI. Los Angeles saw the most dramatic increase of any U.S. city, with doctors writing an average of 16 times more prescriptions than their daily average.
Cases have now been confirmed by state health authorities in New York, Texas, California, South Carolina, Kansas, Massachusetts, Indiana, Ohio, Arizona, Michigan, Nevada, New Jersey, Delaware, Maine, Colorado, Georgia and Minnesota.
Signs of concern abound. Most major U.S. airlines announced Friday that they will temporarily cut back on flights to Mexico to match weak demand. Religious organizations are altering their services this weekend, avoiding activities that call for close contact between congregants. Some churches will not serve communion wine or place wafers in the mouths of congregants because of the risk of swine flu.
Others are looking to profit on the fear. In Indiana, state officials warned of swine flu telephone scams, in which someone pretending to be from the CDC calls offering "mandatory swine flu kits."
Overseas, a U.K. hospital worker is expected to learn today if he is the country's first case of human-to-human transfer of swine flu, according to Nicola Sturgeon, the Scottish health minister.
Twenty-four-year-old Graeme Pacitti is believed to have fallen ill after seeing his friend, newlywed Iain Askham, who contracted the flu along with his wife, Dawn, while on honeymoon in Mexico.
Pacitti has been prescribed the anti-viral drug, Tamiflu, and is being quarantined at home in Falkirk, Scotland.
Speaking to the British newspaper The Daily Telegraph, Pacitti said, "It is just typical flu. I have a sore throat, a sore head and an upset stomach. I am just waiting to be retested again and hope to get more information later today."
The Askhams, U.K.'s first confirmed swine flu cases, have now made a complete recovery and have left Monklands hospital, where they were being treated.
Did an Obama Staffer Bring the Virus to the U.S.?
The Obama administration may have had a brush with the swine flu outbreak after a member of the White House advance team on Obama's recent trip to Mexico apparently came down with the disease.
White House press secretary Robert Gibbs said the staff member, whom he did not identify, began to feel ill April 16 after he accompanied Secretary of Energy Steven Chu to Mexico in advance of Obama's arrival. Two days later, Gibbs said the staff member returned to the United States on a United Airlines flight to Dulles International Airport outside Washington, D.C.
On April 28, the individual's wife, son and nephew tested positive for H1N1, Gibbs said, adding that samples had been sent to the CDC to determine if it is the same strain of H1N1 that now threatens to spark a global pandemic.
Though President Obama was in Mexico at the same time as this individual, Gibbs said the staff member never came within six feet of the president. Neither Obama nor Chu has shown any symptoms, and neither has been tested for the flu.
Gibbs said the staff member likely carried the virus on the flight home from Mexico.
"The family members experienced mild to moderate symptoms, received no medications and recovered," Gibbs said, adding that the individual is back at work now.
The administration staff member tested negative, which Gibbs noted was "likely because so much time had elapsed since the onset of his own symptoms that they would not show up in the test."
On Thursday, the swine flu outbreak caused schools in 14 states to shut their doors on more than 160,000 schoolchildren, and additional closures could affect more than 332,000 students in 21 states
In total, more than 100 school systems have closed at least one school as the nation tries to stifle the spread of the disease.
Richard Besser, acting director of the CDC, said that health officials hoped the closures would help stem the spread of the virus in affected states, although he added that it remained to be seen whether the strategy would actually work.
"We want to make sure that school closure is in fact lowering the risk of spread in a community," Besser told "Good Morning America" Thursday. "The goal is not to send the children out into the community."
Vice President Joe Biden said on "GMA" Thursday that he hoped that parents would be able to make adjustments as their children's schools -- and possibly their own workplaces -- shut down to limit the threat of swine flu spread.
"Our hope is that employers will be generous in how they treat that employee," Biden said.
The school closures cap off several frenzied days of adjustments by federal and state governments to stem the spread of the virus.
New York State Hardest Hit
And the spread appears far from over. A 30-year-old female from Kentucky with a confirmed case of swine flu is currently hospitalized in serious condition at West Georgia Medical Center in LaGrange. The woman had recently traveled to Cancun and was in Georgia for a wedding when she became ill. She has been in the hospital since April 26.
In Washington, D.C., the World Bank issued a statement Thursday morning that a staff member who had traveled to Mexico on business April 14-18 had been "preliminarily diagnosed" with swine flu. The CDC has yet to confirm the diagnosis of that individual, who is a Maryland resident, according to the statement.
The World Health Organization raised its pandemic flu alert again Wednesday to phase 5, which denotes that a pandemic is imminent. On Thursday, WHO reported that the number of lab-confirmed cases worldwide rose to 236, up from 148 on Wednesday.
In Mexico, where the flu outbreak was believed to have started, the government took more drastic action Thursday, ordering all nonessential businesses to close.
Mexican President Felipe Calderon, who has been criticized for his low profile during the crisis, addressed the nation Wednesday night and told Mexicans to stay home.
"There is no safer place to protect yourself against catching swine flu than in your house," he said.
The first death from swine flu in the United States occurred Wednesday, when a 22-month-old baby boy in Texas died.
The worst hit state so far is New York, with 50 confirmed cases.
Mayor Michael Bloomberg originally said Monday that the cases were confined to a "single cluster," to students at St. Francis Preparatory School and their relatives. Several of the students had spent spring break in Cancun, Mexico.
Since then, Bloomberg has confirmed that it had spread to several other schools and that hundreds of children could be suffering from the virus. New York City Health Commissioner Thomas Frieden said that "many hundreds" of students and teachers at St. Francis are sick, although most of those cases appeared mild so far.
"It is here, and it is spreading," Frieden said. "We do not know whether it will continue to spread."
"I do expect more cases and expect more states to be affected," Dr. Anne Schuchat, interim deputy director for the CDC's science and public health program, told a Senate hearing Wednesday. "I think we need to be prepared that even if it starts to look a little better, it may get a little worse."
To fight the epidemic, the Obama administration is asking Congress for $1.5 billion. White House press secretary Gibbs said the president was requesting the funds "out of an abundance of caution" to "enhance our nation's capability to respond to the potential spread of this outbreak."
The CDC has become the center for the swine flu investigation. It is one of only four laboratories in the world that have the expertise to unravel a novel flu strain.
"What we're trying to do is to identify how bad, how good, the swine flu is currently operating -- is it expanding, is it contracting, is it maintaining a steady state," said Phillip Navin, director of the Division of Emergency Operations at the CDC.
With the uptick in cases, the CDC shipped more antivirals and sent additional teams into the field.
"I think at the moment we need to be looking forward and making sure that we're doing everything that we can to keep people from getting sick," said Dr. Steve Reed, director of the CDC's Influenza Coordination Unit.
Swine Flu Ground Zero
With the flu spreading quickly in the United States and across the globe, the actions of Mexican health officials are under the microscope. Many health experts question whether the government has done enough to contain the flu.
Oscar Barrera, who was diagnosed with the flu Monday and prescribed Tamiflu, said he was sent home by medical officials and simply told to keep away from other people.
Barrera claimed that health officials did not test his pregnant wife and three-year-old son, or anyone in the cell phone shop where he worked, for the flu.
"What worries me most is if the officials don't do enough to protect my family," Barrera told ABC News.
According to Mexico's health ministry, there now have been 12 confirmed deaths of the swine flu in Mexico, but roughly 176 deaths are suspected of having been caused by the virus. There are nearly 3,000 suspected cases.
Schools, museums, parks and churches in Mexico City have been shut down by the government. A leading business group estimated that canceled events and closure of establishments to prevent the spread of swine flu is costing Mexico City at least $57 million a day.
All of Mexico's Mayan ruins and Aztec pyramids have also been shut down until further notice.
Mexican officials are hoping the 10-day shutdown will be enough to cover the two-day incubation period and the seven-day recovery of anyone who has the virus.
Mexico's first suspected case of the swine flu was detected in the remote farming village of La Gloria, where 5-year-old Edgar Hernandez contracted the disease nearly one month ago, authorities said.
"The most likely way that this young boy got the infection was from another person who had been in contact with the pigs," said Dr. Kathryn Edwards at Vanderbilt Medical Center.
More than 800 people in the town of 2,000 were infected, authorities said, but no deaths were reported. It took seven days for Mexico to confirm its first cases of swine flu, according to World Health Organization estimates.
Officials said it's still too early to determine how the disease spread from La Gloria into a global health emergency.
The Associated Press contributed to the reporting of this story.