Antibody response of an elderly population to a supplemental dose of influenza B vaccine.

Recent reports have suggested that the antibody response of elderly persons to standard doses of influenza vaccine is depressed. We examined the effect of an additional threefold dose of influenza B vaccine on the antibody response in elderly, ambulatory veterans. One hundred thirty-one male subjects aged 70 years and older were randomized to receive one of three influenza vaccine regimens: Group I received standard trivalent influenza vaccine containing 15 micrograms of B/USSR/100/83 in one arm and placebo in the other; Group II received standard trivalent vaccine in one arm and a supplemental dose of 45 micrograms of B/USSR in the other; Group III received the same dose as group II combined in one arm with a placebo in the other. Antibody levels were measured at baseline, 1 month, and 5 months. Nearly 80% of the participants achieved levels of antibody to B/USSR considered protective; seroconversion rates varied from 40% to 61%. No significant differences in antibody response to B/USSR occurred among the vaccine groups, and there were more side effects at higher doses. The higher dose groups did, however, achieve greater antibody levels to the drifted influenza B virus which circulated during the year of the study. Response to the influenza A components of the vaccine, however, may have been blunted in Group III which received a large dose of A and B antigens all at one site.