Federal officials would not offer specifics about how the newest findings could alter the logistics of a vaccination campaign. The government has spent more than $1 billion for about 190 million doses of the vaccine from five manufacturers. Roughly 40 million doses are expected to be ready by the middle of next month and would be released as they become available.
The preliminary results of the Australian study, published in the New England Journal of Medicine, were similar to the American trials. Australian researchers found that 97 percent of the 240 adults who got one 15-microgram dose developed antibodies to the virus after just 10 days.
The trials were done by vaccine maker CSL, which is licensed to provide millions of doses of the vaccine in the United States.
Using less vaccine means not only being able to stretch supply farther, but it also means cutting down on costs and the frustrating logistics of lining people up for two shots, said Dr. Wilbur Chen, a vaccinologist who is helping to oversee the H1N1 vaccine trials at the University of Maryland's Center for Vaccine Development.
"I was elated when I found out the results," he said. "That was one of the best-case scenarios, seeing this vaccine working in people this well. We can rest much better at night, knowing that we will have more doses and we'll have an easier time to vaccinate the population. It was a headache, honestly, thinking about vaccinating people twice in 21 days. It's hard enough to get people to come back."
The initial trial results leave many unanswered questions. Scientists don't yet know whether one dose will be effective in children or pregnant women - the vaccine is still being tested in the groups. Results in children aren't expected for another two weeks and findings in pregnant women may not come until late October, Fauci said.
It's also unclear whether people with compromised immune systems would benefit from one dose rather than two. That group, along with children and pregnant women, should be at the front of the line for being vaccinated, since they are at most risk for developing serious complications from the virus, the CDC has said.
Researchers are examining ways to further stretch vaccine supply. Chen is heading an NIH-sponsored trial on a vaccine with an immune booster added to it, known as adjuvant, starting Monday at the university.
