The global flu epidemic early last century was possibly the deadliest outbreak of all time. The virus was an H1N1 strain - different from the H1N1 strain involved in the current outbreak - and struck mostly healthy young adults. Experts estimate it killed about 40 to 50 million people worldwide.
"We do not see the markers for virulence that were seen in the 1918 virus," said Dr. Nancy Cox, the Centers for Disease Control and Prevention flu chief.
The CDC said there were now 141 confirmed cases in the U.S., up from 109 on Thursday. The flu is now in 19 states, up from 11, according to federal figures. Separately a few states reported slightly higher numbers.
There is still only one death reported in the U.S. - a Mexican toddler who died in Texas.
Still, in this atmosphere of anxiety, prescriptions for antivirals are up 800 percent since early April, reports CBS News correspondent Nancy Cordes.
And the government is spending $250 million to buy 13 million courses of anti-flu drugs Tamiflu and Relenza.
President Obama explained the move in a special cabinet meeting.
He the swine flu might end up running its course "like ordinary flus" but the government is preparing for the worst just in case. He said the flu is a cause for concern because it is new strain and people have not developed an immunity to it.
"Even if it turns out that H1N1 is relatively mild on front end could come back in more virulent form during flu season," Mr. Obama said.
Mr. Obama said, "I'm optimistic that we're going to be able to manage this effectively."
Still,, some public health experts are expressing concern about whether hospitals could handle the onslaught if the outbreak worsens in the near future or in the next flu season.
"We really have not made much progress in our hospitals in the us being able to surge up to increase capacity in a hurry to accommodate lots of sick patients from influenza," Dr. Irwin Redlener, director of the National Center for Disaster Preparedness at Columbia University, told Cordes.
The man spearheading flu preps at health and human services says hospitals will never have enough beds to handle a pandemic.
"It's just not cost effective to build those facilities and have them sit empty," said Rear Adm. Craig Vanderwagen, Assistant Secretary for Preparedness and Response at the Department of Health and Human Services.
But he's confident that there are enough medical supplies and doctors. And he pointed out they can be shifted around the country - from areas where the virus has not struck to ones where there are active cases - as needed, Cordes reports.
Amid the growing concern over the virus, federal officials are also warning Americans of fraudulent H1N1 treatments advertised over the Internet.
Some sites are promoting unauthorized products that claim to diagnose, prevent, treat or cure the flu strain, according the Food and Drug Administration and the Federal Trade Commission.
"The last thing any consumer needs right now is to be conned by someone selling fraudulent flu remedies," said FTC Chairman Jon Leibowitz in a statement.
U.S. authorities pledged to eventually produce enough swine flu vaccine for everyone who needs it but the shots couldn't begin until fall at the earliest.
Within a week, the CDC hopes to send samples of the new virus to manufacturers so they can begin. But there's no green light yet for actual vaccine production, reports CBS News medical correspondent Dr. Jon LaPook.
"We anticipate that when we decide to manufacture a vaccine, we will have a large quantity of vaccine by the fall," Dr. Richard Besser, acting director of the Centers for Disease Control and Prevention, told CBS News.
Federal officials also tried to reassure the public it's still safe to fly and ride public transportation after Vice President Joe Biden said he wouldn't recommend it to his family.
"There's not an increased risk there," the CDC's Besser said Friday. "If you have the flu or flu-like symptoms, you shouldn't be getting on an airplane or you shouldn't be getting in the subway, but for the general population that's quite fine to do," he said.
On airplanes, air circulates side to side, with air entering the cabin from overhead, circulating across the aircraft and then exiting the cabin near the floor, reports CBS News correspondent Bianca Solorzano.
"The air goes out the sides of the plane and up through HEPA filters, which are hospital filters. The air on a plane is cleaner than the air in my building," Roger Dow, president of the U.S. Travel Association, told CBS News.
But concerns about the flu were enough to divert one airplane bound for Washington, DC today, Cordes reports. A passenger from Germany complained she felt ill. And the pilots landed right away in Boston.
Separately, despite assurances that air travel was safe, Houston-based Continental Airlines, which has over 500 flights per week between the U.S. and Mexico, became the first U.S. carrier to curtail service. Many travelers have become increasingly concerned about going to Mexico, though authorities there said new cases and the death rate was leveling off.
Mexico has confirmed 397 swine flu cases but stopped reporting suspected infections when the number approached 2,500. Mexico late Friday raised the number of confirmed deaths from the flu to 16, although reports have indicated that roughly 120 may have died from it.
"We were already experiencing soft market conditions due to the economy, and now our Mexico routes in particular have extra weakness," Continental Chairman and Chief Executive Larry Kellner said in a statement Friday.
It wasn't immediately clear whether other airlines would follow Continental's lead. "We are hearing that there is a softening of demand to and from Mexico," said David Castelveter, a spokesman for the Air Transportation Association, which represents airlines.
Meanwhile, Mexico's chief epidemiologist said the World Health Organization wasto its warning about a health crisis that turned into a global swine flu scare and he wants an investigation.
Clinics and hospital emergency rooms in New York, California and some other states are seeing a surge in patients with coughs and sneezes that might have been ignored before the outbreak.
In Washington state, a 33-year-old pediatrician with allergy symptoms saw patients before she became ill enough to seek treatment, reports CBS News correspondent Nancy Cordes. With official test results pending, health officials believe she has the H1N1 virus and are in the process of contacting all the patients she saw on Monday.
Scientists were racing to prepare the key ingredient to make a vaccine against the never-before-seen flu strain - if it's ultimately needed. But it will take several months before the first pilot lots begin required human testing to ensure the vaccine is safe and effective. If all goes well, broader production could start in the fall.
"We think 600 million doses is achievable in a six-month time frame" from that fall start, Health and Human Services Assistant Secretary Craig Vanderwagen told lawmakers Thursday.
"I don't want anybody to have false expectations. The science is challenging here," Vanderwagen told reporters. "Production can be done, robust production capacity is there. It's a question of can we get the science worked on the specifics of this vaccine."
Until a vaccine is ready, the government has stockpiled anti-viral medications that can ease flu symptoms or help prevent infection. The medicines are proving effective.
The government is purchasing 13 million additional courses of Tamiflu and Relenza, antiviral flu medications to replace the millions it has distributed to the affected states, reports Cordes.
It's also sending 400,000 courses to Mexico to assist with the outbreak there.
More than half the states have yet to stockpile the number of flu-treatment doses recommended by the federal government, an Associated Press survey found. They cited budget contraints or said it's better to spend health-care funds on preventing the spread of disease than on antiviral medicines that may or may not work on a particular flu strain.
But, the acting head of the U.S. Centers for Disease Control and Prevention said no state is expected to experience shortages because the federal government is racing to fill states' stockpiles with millions of additional doses from its own strategic reserves.
The swine flu outbreak penetrated over 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 Barack 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.
The Washington Post identified the aide as Marc Griswold, a former Secret Service agent who was doing advance work for Chu. It said that Griswold has complained about the infection placing his family in an awkward position with family and neighbors.
"We're not the Typhoid Mary family, for goodness sake," he said. "We've been told that we're not contagious. We're already past the seven-day mark for that."
So far U.S. cases are mostly fairly mild with one death, unlike in Mexico where more than 160 suspected deaths have been reported. Most of the U.S. cases so far haven't needed a doctor's care, officials said.
There are 146 confirmed cases in the United States, including 50 in New York; 28 in Texas; 18 in California; 16 in South Carolina; five in New Jersey; four each in Arizona and Delaware; three each in Indiana and Illinois; two each in Kansas, Colorado, Virginia, Michigan and Massachusetts; and one each in Ohio, Minnesota, Nebraska, Nevada and Kentucky.
Around the world, France, Switzerland and the Netherlands became the latest countries to report infections.
According to news reports, South Korea has its first confirmed case. Yonhap news agency reported Saturday that final tests confirmed a 51-year-old woman has the disease after recently returning from a trip to Mexico.
She has been listed as a probable case since Tuesday. Officials have said she has recovered enough to consider being discharged from a hospital where she remains quarantined.
Officials declined to confirm the report, saying they will make a formal announcement later.
France's health minister said the patients, a 49-year-old man and a 24-year-old woman, both recently returned from Mexico. Roselyne Bachelot said Friday both are "doing well." They are hospitalized in Paris.
Bachelot also said another patient "very probably" had the virus, though it has not yet been confirmed.
Canada, New Zealand, Britain, Germany, Spain, Israel and Austria also have confirmed cases.
The Red Cross said it was readying an army of 60 million volunteers who could be deployed around the world to help slow the virus' spread.
2009 H1N1 Flu Outbreak Map:
This is a map depicting confirmed and suspected cases of the 2009 H1N1 outbreak, with contributors from all over the world, from a variety of backgrounds including health, journalism, technology.