Seasonal flu vaccine offers some protection from H5N1

The yearly influenza vaccine that health officials urge people to get each fall might also offer certain individuals some cross protection against the H5N1 virus commonly known as bird flu, according to investigators at St. Jude Children's Research Hospital.

The investigators found that the virus protein N1, one of two or more proteins present in the annual influenza shot, can act as a vaccine itself and trigger some cross protection against H5N1 in mice; and that some human volunteers already had antibodies directed against the same part of this virus.

"The jury is still out on whether the seasonal influenza vaccine is definitely a reliable way to offer people some protection from H5N1," said Richard J. Webby, Ph.D., assistant member in the Virology division of the Department of Infectious Diseases at St. Jude. "But our initial results suggest to us that this is a research trail worth following." Webby is senior author of the report that appears in the Feb. 13 issue of the online journal PLoS Medicine at www.plosmedicine.org.

The key to the apparent cross protection against H5N1 provided by the human influenza vaccine appears to be the antibodies produced in response to N1, a variety of the protein neuraminidase-one of the two proteins on the surface of the virus. While the amount of the other protein in the vaccine, hemagglutinin, or "H," occurs in large amounts, the amount of N1 can vary widely depending on the company that produces the vaccine.

If the initial findings of the St. Jude study are confirmed in the future, there may be a greater interest in examining the amount of neuraminidase in yearly influenza vaccines, according to Matthew Sandbulte, Ph.D., a post- doctoral fellow at the Food and Drug Administration, who did much of the work on this project. "Hemagglutinin is more abundant than neuraminidase on viruses and is a better target for protective immunity, so current vaccines are designed to trigger immune responses mostly to hemagglutinin," he said. "That is why vaccines contain standard amounts of hemagglutinin, but varying amounts of neuraminidase. But if further research confirms that the N1 part of the influenza vaccine offers some cross protection against H5N1, it will be desirable to have a better idea of the amount of N1 present in these vaccines."

Other authors of this study include Adrianus C. M. Boon (St. Jude); Gretchen S. Jimenez and Larry R. Smith (Vical, San Diego, Calif.) and John J. Treanor (University of Rochester, Rochester, N.Y.).

This work was supported in part by the National Institute of Allergy and Infectious Disease (National Institutes of Health) and ALSAC.