POSSIBLE CORRELATION BETWEEN LOW ANTIGENIC DRIFT OF A(H1N1) INFLUENZA-VIRUSES AND INDUCTION OF HI ANTIBODIES

This study examined whether, during a seven-year period of low A(H1N1) influenza virus antigenic drift (1988-1989 and 1994-1995, winters), h umoral antibody response of elderly volunteers to influenza vaccines c ould suggest a lack of antibody pressure for drift. In all the years s tudied A/Taiwan/1/86, the A(H1N1) vaccine component, had a low ability to induce protective hemagglutination-inhibiting (HI) antibody titres (greater than or equal to 1:40). However a similar low immunogenicity was found for some of the different A(H3N2) strain variants of influe nza virus, co-circulating in the same period and showing a Although ou r data could be at least in part explained by the type of study popula tion (elderly and repeatedly vaccinated), postepidemic serological stu dies did not evidence a consistently lower ability in mounting protect ive immune response in elderly people as compared with younger against the influenza strains studied. Therefore, our present results did not exclude a true low immunogenicity of A/Taiwan and of some A(H3N2) inf luenza strains, circulating in the winters examined. This suggests tha t, besides the necessity to evade prior immunity, additional factors c ould influence the frequency of influenza viruses antigenic drifts.