A U.S. health official says the new swine flu virus lacks genes that made the 1918 pandemic strain so deadly.
The Centers for Disease Control and Prevention said Friday the new virus is "a very unusual" four-way combination of human genes and genes from swine viruses found in North America, Asia and Europe.
CDC flu chief Dr. Nancy Cox said the good news is "we do not see the markers for virulence that were seen in the 1918 virus."
U.S. authorities are pledging to eventually produce enough swine flu vaccine for everyone but the shots won't begin until fall at the earliest.
Scientists are racing to prepare the key ingredient to make a vaccine against the never-before-seen flu strain — if it's ultimately needed.
10 Ways to Prevent Swine FluBut it will take several months before the first pilot lots begin required human testing to ensure the vaccine is safe and effective.
"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 said.
"I don't want anybody to have false expectations. The science is challenging here," Vanderwagen told reporters. "t's a question of can we get the science worked on the specifics of this vaccine."
The Centers for Disease Control and Prevention have reported 141 cases of swine flu in 19 states. Some 300 schools have closed in communities across the country as health authorities work to contain the virus.
On Friday, the World Health Organization raised its tally of confirmed human cases to 331, up from 257.
Cox said the manufacture of a vaccine for the new virus would not interfere with the manufacture of a seasonal flu vaccine for the upcoming flu season. She said that, if it becomes necessary to make a supplemental swine flu vaccine, that vaccine would be prepared "in parallel" with the seasonal vaccine.
Because of this, world scientists are in agreement, for now, that the seasonal vaccine offers no protection, she said.
"We have no doubt making a successful vaccine is possible," Kieny said.
The reason why the vaccine will take so long to produce is because scientists must first isolate the virus and then adapt it to be made into a vaccine. It is believed that the adapted virus should be ready by the end of May. After this, the virus is injected into eggs where it will grow. From there, scientists will remove it, kill it and then formulate it into a vaccine.
After that,
clinical trials in humans must be performed to ensure it's safety and effectiveness. Later, it will need to receive approval by national regulatory authorities, Kieny said.
The WHO is now reporting 11 countries have confirmed cases, including Germany, which confirmed Friday the first case of swine flu transmission within the country. This does not include Hong Kong and Denmark, which confirmed cases mid-morning Friday.
Federal officials had to spend much of Thursday reassuring 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," Dr. Richard Besser, acting director of the CDC, 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.
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.
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.
Reassurances from top health officials didn't stop the questions from coming.
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, Besser said. 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.
The NumbersAlthough the CDC has tallied just 141 swine flu cases in the U.S., state health experts say the count is likely much higher. Among the U.S. cases confirmed by the Centers for Disease Control and Prevention are 51 in New York, 16 in Texas and 14 in California, as well as scattered cases in Kansas, Illinois, Florida, Massachusetts, Michigan, Arizona, Indiana, Nevada, Ohio, Maine and South Carolina.
State officials also confirmed cases in Minnesota, Georgia, Delaware,
Utah, New Jersey, Virginia and Colorado.
About 300 of the nation's
132,000 schools have closed, while high school, college and professional sporting events have been called off nationwide due to increasing fears.
Nebraska's chief medical officer says federal tests have confirmed the first case of swine flu in the state. It involves a California man in his 40s who's vacationing in the Omaha area. Health officials have said the infection ultimately will be reported as a California case because the CDC counts cases of infectious disease by residence. Nebraska also has suspected cases of the flu.
Wisconsin Gov. Jim Doyle declared a public health emergency after two more probable cases of swine flu were identified in Wisconsin Thursday.
Thirty-nine Marines were confined to their base in California after one came down with the disease.
A pediatrician in Washington state saw 22 patients with flu-like symptoms before she developed serious symptoms and went to the emergency room. The Pennsylvania Department of Health says it continues to find people who it considers to be probable swine flu cases. It is investigating three new possible cases.
Illinois health officials say the number of probable swine flu cases in the state has more than doubled to 41.
A security aide helping with arrangements during President Barack Obama's recent trip to Mexico became sick with flu-like symptoms and three members of his family later contracted probable swine flu, the White House said Thursday.
White House press secretary Robert Gibbs remained steadfast that the president was never at risk of contracting the flu.
It was also learned that a Mexican toddler who visited Texas with his family and died Monday night in Houston, spent a day with his family shopping at a huge Houston indoor mall the day before he began to show symptoms, said Cameron County Judge Carlos Cascos, who interviewed the boy's family.
Slippery Rock University in Pennsylvania will hold a separate graduation for 22 students who recently returned from Mexico.
So far, the students are in good health, but school officials fear they could have been exposed to the swine flu. Commencement falls in the middle of an incubation period during which the students have been advised to limit contact with others. The students were in Mexico completing their student-teacher requirements.
Even though scientists say the new virus is more pig than human, the WHO said it plans to no longer call it "swine flu" to avoid confusion over the risk from pigs and eating pork. Health officials have stressed repeatedly that the disease is being transmitted human to human and that there is no risk from eating pork.
WHO spokesman Dick Thompson says the name change comes after the agriculture industry and the U.N. food agency expressed concerns that the term "swine flu" was misleading consumers and needlessly causing countries to order the slaughter of pigs.
He told reporters in Geneva "we're going to stick with the technical scientific name H1N1 influenza A."
Several countries have put a ban a pork imports. Hog futures fell for the sixth time in seven sessions on Thursday because of continued speculation that people will stop eating pork.
On Wednesday, the WHO boosted its alert level to one level below a full-fledged pandemic. The new 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.
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, Spain, Israel and Austria.
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.
Where Did Virus Originate?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.
California is now being eyed as the potential source of the virus.
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.
Swine Flu TimelineOne 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.
The Associated Press and Reuters contributed to this report.
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