Persistence of influenza A/New Jersey/76 (Hsw1N1) antibody one year after vaccination.

Serum HI and neuraminidase-inhibiting (NI) antibody measurements were made at 3, 32 and 50 weeks after inactivated influenza Hsw1N1 vaccination of 438 adults in 1976. Although the highest postvaccination geometric mean HI titers were observed in persons greater than or equal to 52 years of age, the rate of antibody decline was similar in adults of all ages. In 14 children who had a seroconversion following two doses of whole virus or split virus vaccine, the geometric mean HI antibody titer was lower after the second vaccine dose than the peak titer observed in adults, and the decrease in titer was also more rapid by 4 to 7 months. One year after influenza Hsw1N1 vaccination of adults, the prevalence of homologous HI antibody greater than or equal to 40 was 71% to 97%, whereas only two of the 14 children maintained similar titers at 5 to 7 months. Neuraminidase-inhibiting antibody titer formation occurred more frequently in those without prevaccination NI antibody, but the rate of decline was also greatest in this initially seronegative group. The rate of antibody decline at one year in the population with preexisting antibody was similar to that observed for HI antibody decline in a primed population. Heterologous influenza A/Victoria/3/75 (H3N2) HI antibody formation occurred in 22% of adults aged 25 to 51 after Hsw1N1 vaccination and in 12% of those over the age of 51, but the rate of heterologous antibody decline was more rapid than that observed for homologous antibody.