NEW YORK, UNITED STATES - Hepatitis A infections, usually transmitted via contaminated food, can cause debilitating illness, but protection afforded by the hepatitis A vaccine last more than a decade, a new study shows.

In fact, antibodies against hepatitis A virus persist for up to 27 years after vaccination, report investigators from the Centers for Disease Control and Prevention in Atlanta and the Alaska Native Tribal Health Consortium in Anchorage.

Lead author Dr. Laura L. Hammitt, now at the Kenya Medical Research Institute/Welcome Trust Collaboration in Kilifi, and colleagues enrolled 144 children and 128 adults who responded to a three-shot series of hepatitis A vaccine to assess the persistence of antibodies.

The adults had received a primary dose of hepatitis A vaccine, with a second vaccination given 1 month later and a third given 12 months after the first.

The children were between 3 and 6 years of age and were given three doses at various intervals over the course of a year.

Hammitt's team collected blood samples 1 month after vaccination and again 1 to 10 years after vaccination to test for anti-hepatitis A antibodies. The researchers calculated long-term antibody persistence based on the observed rate of decline in concentrations.

"The estimated duration of antibody persistence was 21-27 years, depending on the vaccination schedule," Hammitt and colleagues write in the Journal of Infectious Diseases.

They say the findings show that protective levels of anti-hepatitis A antibodies are retained for at least 10 years after vaccination. "Hepatitis A booster doses after completion of the primary vaccination series do not appear to be warranted and are not currently recommended," the CDC team advises.

Nonetheless, they point out, antibody concentrations do decline over time and ongoing monitoring is needed "to assess whether persons vaccinated as children will be protected throughout adulthood."

SOURCE: Journal of Infectious Diseases, December 15, 2008.