Long-term efficacy of oil-adjuvant influenza vaccine in an industrial population.

Hobson, Lane, Beare, and Chivers (I964) found high haemagglutination-inhibiting (H.I.) antibody titres in the sera of almost half their volunteers who had been inoculated with an oil-adjuvant influenza vaccine more than two years previously. The antibody titres which were found suggest that if artificially induced antibodies are as effective as naturally acquired antibodies (a supposition by no means proven), the clinical protection offered by such vaccines may well extend to three years or longer. Davenport, Hennessy, and Bell (I962) pointed out that, with adjuvant vaccines, antibody levels of from a quarter to a half of the maximum attained have been found eight to nine years after inoculation. Himmelweit (I963) suggested that, because of the efficacy of these vaccines, inoculation of a substantial part of the general population every three to five years might be sufficient to build up a herd immunity against prevalent viruses. However, such suggestions are based largely on serological evidence, and there has been no general confirmation in this country based on large-scale clinical trials. Howell and Stott (I964) reported a trial of oiladjuvant vaccine in I,679 employees at two U.K. Atomic Energy Establishments (Springfields and Dounreay). The occurrence of a mild influenza epidemic of mixed A and B strains in the early part of I966, more than two years after the inoculation ofthese employees, suggested that an attempt should be made to discover whether the vaccinated group