Fighting the H1N1 flu virus, otherwise known as swine flu, may have gotten more manageable.
Australian and U.S. researchers said Thursday that one dose of the new swine flu vaccine looks strong enough to protect adults - and can begin protection within 10 days of the shot.
Australian shot maker CSL Ltd. published results of a study that found 75 per cent to 96 per cent of vaccinated people should be protected with one dose - the same degree of effectiveness as the regular winter flu shot. That's remarkable considering scientists thought it would take two doses.
U.S. data to be released Friday confirm those findings and show the protection starts rapidly, Dr. Anthony Fauci of the National Institutes of Health told The Associated Press.
"This is quite good news," Fauci said.
CBSNews.com Special Report: H1N1
The dose question has an important ramification: It means people will have to line up for influenza vaccinations twice this year instead of three times - once for the regular winter flu shot and a second time to be inoculated against swine flu, what doctors call the 2009 H1N1 strain.
Thursday's swine flu vaccine reports center on adults; studies in children are not finished yet.
But scientists had feared that people of all ages would need two shots about a month apart because the new H1N1 strain is so genetically different from normally circulating flu strains that most of the population has little if any immunity.
Chinese manufacturers a week ago that one dose could be enough. But different manufacturers make different formulations of the vaccine, so more evidence was needed.
Thus the CSL study, rushed out by the New England Journal of Medicine late Thursday, is welcome news. In a study of 240 adults, half younger than 50 and half over, one shot prompted the same kind of immune response indicating protection that is seen with regular flu vaccine. And a standard 15-microgram dose - not the double dose that also was tested - was enough.
CSL, which is one U.S. vaccine supplier, found the same side effects in its study that people experience with regular flu vaccine, which is no surprise since this shot is merely a recipe change from the annual standby. About 45 per cent of recipients had mild reactions such as a headache, sore arm or redness at the shot site.
On Friday, the NIH is set to release results of its own studies of hundreds of adults that confirm that one shot works, Fauci said. Plus, the U.S. work shows that people are protected eight to 10 days after that inoculation, he said.
One dose means tight supplies of H1N1 vaccine won't be stretched so badly after all. The U.S. has ordered 195 million doses, based on the hope that 15 micrograms was indeed the right dose. Had it taken twice that dose, or two shots apiece, half as many people could have received the vaccine.
The winter flu vaccine is widely available now, and U.S. health authorities urged people to get it out of the way now before swine flu shots start arriving in mid-October.
Despite all the headlines about swine flu, which has become the main influenza strain circulating in the world, doctors do expect some garden-variety flu to hit this fall too - the kind that every year kills 36,000 Americans and hospitalizes 200,000.
"Take some individual responsibility to stay healthy during the flu season," said Health and Human Services Secretary Kathleen Sebelius, who scheduled her own seasonal shot for Friday. Waiting to get the first inoculation out of the way "is not in anybody's best interest," added Dr. Nancy Nielsen, past president of the American Medical Association. She said busy doctors need to have completed regular vaccinations by the time they have to deal with H1N1 shots.
Waiting to get the first inoculation out of the way "is not in anybody's best interest," added Dr. Nancy Nielsen, past president of the American Medical Association. She said busy doctors need to have completed regular vaccinations by the time they have to deal with H1N1 shots.
There's no way to predict how much of either flu strain will circulate.
"This year, we are in uncharted territory," warned Dr. Thomas Frieden, director of the Centers for Disease Control and Prevention.
He said some parts of the Southeast in the past few weeks have experienced as much flu as is usually seen in the middle of winter. So far, it's all the H1N1 variety, with schools and colleges experiencing outbreaks almost as soon as classes began.
Indeed, a typical school student who catches swine flu will spread it to two to three classmates, says a stark new estimate published Thursday in the journal Science. Flu specialist Ira Longini of the University of Washington in Seattle based the estimate on how swine flu spread through a New York City school in April, and some other schools since.
A separate report in Thursday's New England Journal suggested European manufacturers might get away with an even smaller dose. Novartis Vaccines added what's called an adjuvant, or immune-boosting chemical, to its version of the swine flu shot and found a 7.5-microgram dose was effective. It did, however, spark more of those reactions like injection-site pain.
Numerous countries allow flu vaccines with adjuvants to sell every year, but the U.S. has never approved an adjuvant-containing flu shot.