Influenza revaccination of elderly travelers: antibody response to single influenza vaccination and revaccination at 12 weeks.

The antibody response to a single influenza vaccination and the effect of influenza revaccination was assessed in healthy elderly persons. Travelers > or =65 years old who had received influenza vaccine before travel were enrolled in the study and were offered a second vaccination after 12 weeks. Geographic and age-matched control subjects received a single vaccination. A second influenza vaccination was not associated with increased adverse effects. There was no significant difference between log(10) hemagglutinin-inhibiting (HI) antibody titers or an HI antibody titer > or =1:40 (considered to be protective) in 28 control subjects and 28 revaccinated travelers for any antigen. Probable protection for influenza A antigens remained high 24 weeks after a single immunization and revaccination (A/Sydney/05/97 [H3N2], 92% and 96%, and A/Beijing/262/95 [H1N1], 80% and 96%, respectively). Response to B/Harbin was less throughout the study. A/Sydney antibody titer was lower with more times vaccinated in the previous 5 years. Therefore, a second vaccine did not enhance the immune response.