Antibody Induction and Frequency of Adverse Reactions to Influenza Vaccines in the Elderly

A total of 1,223 elderly people in nursing homes in Niigata Prefecture, Japan, were immunized with one or two doses of commercial trivalent split vaccine formulation, against strains including A/HN, A/H3N2 and B for three seasons (1996-1999). The frequencies of adverse reactions and antibody induction were assessed. Frequent side effects of vaccination were local reactions such as redness and tenderness at the site of injection, but there were no serious reactions, suggesting that the vaccine was quite safe for the elderly. Furthermore, antibody induction by immunization was relatively high and independent of the degree of activities of daily living (ADL). Annual repeated influenza vaccination did not diminish protection against influenza. However, antibody induction against antigens was insufficient in the 1997/1998 season, and further improvement in the combination of quantities of the four included antigens may by required. A booster dose after the first dose did not enhance immune responses in the nursing staff, and the one dose method appeared to be indicated for the elderly.