New evidence suggests that a booster vaccination against H5N1 avian influenza given years after initial vaccination with a different strain may prove useful in controlling a potential future pandemic. The study is published in The Journal of Infectious Diseases, now available online.

H5N1 continues to pose a major health risk to birds and humans. As of mid-June, more than 60 percent of the more than 380 human cases have been fatal, and hundreds of millions of birds have died or been culled to prevent the spread of the disease.  Should the virus evolve making human-to-human transmission more likely, a destructive global influenza pandemic could result.

The cornerstone of planning for such a possible pandemic is the development and distribution of effective vaccines. Several vaccines have been developed, but as the virus continues to mutate into genetically distinct lineages, or clades, the problem arises as to whether vaccines based on an older clade will be effective against newer versions.  The new study is the first to report that giving one dose of a newer-clade vaccine to those who were vaccinated previously with older versions is more effective than giving only doses of the newer vaccine to unvaccinated subjects.

The study, conducted by Nega Ali Goji, MD, and colleagues from New York, Maryland, and Alabama, gave a single booster dose of a vaccine based on a clade 1 H5N1 virus circulating in Vietnam in 2004 to subjects who eight years earlier had received two doses of a vaccine based on the original, clade 0 virus that appeared in Hong Kong in 1997.  Sixty-four percent had a positive immune response, which compares favorably to the results of a previous study using two doses of the clade 1 Vietnam virus, in which only 43 percent of those vaccinated had a positive immune response.

Release date: July 16, 2008
Source: Infectious Diseases Society of America