Antibody responses in elderly to influenza vaccination in case of an antigenic mismatch

Background: The vigour of immune responses declines at higher ages. The present study examined sera from influenza vaccinees to assess the magnitude of this effect in case of an antigenic mismatch. Methods: Sera taken in mid-1997 from influenza vaccinees of various ages, including residents of nursing homes, were used in haemagglutination inhibition (HI) tests. In the following influenza season of 1997/1998, a major antigenic mismatch of the H3N2 vaccine component occurred. Results: At advanced age, the homologous antibody response was lowered, starting above 60 years. Also, the cross-reactivity of the formed antibodies to the drifted field virus decreased with age, starting above 70 years. Conclusion: The effect of ageing on the induction of “protective” titres (≥40) of HI antibodies against an emerging deviant strain can be severe: in the 1997/1998 season, above 80 years, the percentage of vaccinees acquiring such titres against the major epidemic H3N2 virus was only about 15%.