The FDA has approved the first vaccine designed to protect humans against the H5N1 avian influenza virus, commonly known as bird flu. Added to the federal government's national stockpile, the vaccine would become available if the H5N1 virus begins to spread easily from human to human. It would be expected to provide people with early but limited protection while a vaccine tailored to the specific viral strain is developed and produced.

The vaccine, given in two I.M. injections spaced about 1 month apart, is approved for adults ages 18 to 64. Generally well tolerated, it may cause minor transitory adverse reactions such as injection site pain, headache, general ill feeling, and muscle pain. In trials, 45% of people who received the two-dose regimen developed antibodies at levels expected to reduce the risk of infection.

To date, no cases of human H5N1 infection have been reported in the United States. Worldwide, about 300 people have been infected with the virus since 2003 and about half died.