HI ANTIBODY KINETICS IN ADULT VOLUNTEERS IMMUNIZED REPEATEDLY WITH INACTIVATED TRIVALENT INFLUENZA VACCINE IN 1990-1992

Volunteer were immunized once, twice or three times in 1990-1992 with commercial trivalent inactivated influenza vaccine and monitored for h aemagglutination inhibition (HI) antibodies. The antibodies that alrea dy existed when the subjects entered the study derived from natural in fections. Immunizations in the second and third years were necessary t o maintain the geometric mean titres of antibody and protection rates at the level recorded after the first vaccination. Negative correlatio ns between prevaccination antibody titres and mean fold antibody incre ases were noted in most instances analysed Moreover, at each individua l prevaccination titre level the mean fold antibody increases and even postvaccination mean titres Mere higher after the first than after su bsequent vaccinations, suggesting that the HI antibody responses might be affected by vaccine-induced pre-existing antibody more than by the same titres of antibody derived from natural infections. This was mos t obvious for antibody to the H1N1 subtype virus, A/Finland/164/91. In immunization with B/Yamagata/16/88, anamnestic response of antibody t o B/Finland/ 150/90, which belongs to the antigenically distinct linea ge of B/Victoria/2/87-like viruses, was more frequent in the first tha n in subsequent years. This is in contrast to homologous antibodies, w hich increased significantly after the second vaccination.