The hepatitis B vaccine - given to protect against infection by a virus that can cause severe liver damage and cancer - may protect for more than two decades, according to a new study.

In 1981, Dr. Brian J. McMahon, from the Alaska Native Medical Center, Anchorage, and his colleagues gave more than 1500 Alaska Native adults and children over age 6 months three doses of hepatitis B vaccine. Before the hepatitis B vaccine was licensed for U.S. use in 1981, as many as one in 12 Alaskan Natives were infected.

In 2003, the team checked with almost 500 of those given the shots and had a response to them at the time to see who was still showing evidence of an immune system response. Blood tests found that more than half - 60 percent - were still considered immune to the virus.

To test whether the other 40 percent were immune, they were given a booster dose of the vaccine, to simulate infection. Most of those people - more than 80 percent - showed a response.

Overall, the researchers estimate that more than 90 percent of the original group was protected. There were no long-term hepatitis B infections in the group, which also suggests a high level of protection, they note in a report in the Journal of Infectious Diseases.

They conclude, “in light of the strong evidence we present here, hepatitis B vaccine booster doses are not currently indicated.”

SOURCE: Journal of Infectious Diseases, November 1, 2009.