The vaccine, which the United States already is stockpiling in the event of a pandemic, was given to 451 healthy adults between the ages 18 and 64, making it the largest such study to date.
[...] Of the participants given two shots of the highest dose of the vaccine 28 days apart, only 54 percent of them had adequate protection from the virus when researchers tested their blood for antibody response. Not all participants were given the same dosage.
Researchers were trying to determine if the vaccine is safe and what dosage would provide sufficient protection from the virus should it become pandemic. The ongoing clinical trials are being funded by the National Institutes of Health.
[...] the study, published in the March 30 edition of the New England Journal of Medicine, shows that while the shot is safe, only about half of those receiving the highest dose of the vaccine -- 90 micrograms -- produced enough antibodies to stave off H5N1 bird flu, if they were exposed.
The seasonal flu shot, by comparison, provides adequate protection in 70 to 90 percent of those receiving one 15-microgram dose of the vaccine.