Characterization of antibody responses to annual influenza vaccination over four years in a healthy elderly population

The effects of yearly influenza immunization on the level of antibody respo nses were assessed in 92 healthy elderly subjects immunized over four conti guous years (1993-1996) with a trivalent influenza vaccine that included A/ Texas annually. Anti-Al Texas antibodies increased significantly and simila rly post-vaccination each year, but returned to comparable baseline levels annually. Percentages of subjects with anti-A/Texas titers greater than or equal to 40 post-vaccination were comparable over four years. Importantly, post-vaccination titers greater than or equal to 40 to A/Texas in 1993 -199 4 predicted anti-A/Texas titers greater than or equal to 40 in subsequent y ears. Thirty percent of individuals produced four-fold rises to any vaccine component the first year it was included in the vaccine, however, this per centage decreased to about 10% after subsequent vaccination with the same c omponent. This study clearly supports the concept that annual immunization with the same influenza vaccine component over multiple years does not sign ificantly decrease antibody titers in a healthy elderly population. (C) 200 1 Elsevier Science Ltd. All rights reserved.