Role for antibody to neuraminidase in protecting against. influenza.

The efficacy of influenza vaccines could be enhanced by selecting strains t hat produce an antigenically adequate neuraminidase and by introducing an o ptimal amount of NA antigen into the vaccine. The monoclonal antibodies to neuraminidase N2 produced by strain A/Beijing/32/92 inhibit the neuraminida se and neutralize the cellular infection either early (group 2 antibodies) or late (group I antibodies) during the cycle. Although the neutralizing ef fect is specific of the homologous variant, it is significantly increased b y combined use of group I and II antibodies. The threat of an influenza pan demic due to emergence in 1997 of the chicken strain A/HongKong/156/97 carr ying an HA (H5 subtype) unrecognized by the human immune system led to inte nsive research efforts that succeeded in characterizing the N1 of H5N1 comp aratively with the other N1s produced by human, porcine, and avian strains. Also, studies were done to look for antibody to the N1 of H5N1 in humans a ccording to age and immunization history, and the neutralizing (i.e., prote ctive) effect of antibody was investigated. It was found that the N1 of H5N 1 shared considerable antigenic similarity with the N1 of porcine strains i solated in 1931 and from 1982 to 1989. In subjects 75 years of age and olde r, antibody to the N1 of H5N1 was highly prevalent and exhibited a potent n eutralizing effect. It follows that subjects aged 75 years or older are pro bably not a top priority group for anti-H5N 1 immunization in the event of a pandemic threat.