Twice as many adults could get the swine flu vaccine as scientists initially expected because the inoculation works in just one dose instead of two, federal officials announced Friday.
The preliminary data from American clinical trials of a vaccine come as a surprise and a relief to public health experts who feared there would not be enough vaccine to reach everyone who would need it.
The data confirm results from an Australian study released Thursday that also found that one dose is effective.
"This is very good news for the vaccination program, both with regard to the supply of the vaccine and its potential efficacy," said Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health. The agency is funding the American trials of two vaccines, one from drugmaker Sanofi Pasteur and another from CSL Ltd.
In the Sanofi vaccine tests, NIH scientists found that 96 percent of healthy adults ages 18 to 64 developed an immune response just eight days after receiving one 15-microgram shot. The percentage was lower in the elderly - 56 percent in people 65 and older. The CSL vaccine yielded similar results - 80 percent of adults 18 to 64 developed an immune response with one 15-microgram dose, while 60 percent of adults 65 and older did.
Fauci said researchers were not surprised that the elderly developed less of an immune response - the figures were similar to the response found when the elderly are given the seasonal flu shot. "Of course, we want to study that - can we ever make that better?" he said. "But it's right now right in the ballpark of what is the immune response in elderly individuals."
The data come from studies being conducted at the University of Maryland's Center for Vaccine Development and a handful of other academic centers nationwide that began testing the experimental vaccine on adults and children last month in a race to launch a mass vaccination campaign expected to start in mid-October.
Developing a safe and effective vaccine is crucial in the government's fight against the pandemic, which began with outbreaks in Mexico this spring and has killed 593 people nationwide - 3,205 around the globe - according to estimates by the federal Centers for Disease Control and Prevention and the World Health Organization.
Infectious disease experts have warned of an onslaught of the virus this fall and are bracing for the possibility that it could mutate and become deadlier.
