Studies on the Efficacy of a Complex Vaccine against Influenza A

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Abstract
Field tests with a complex vaccine prepared from chick embryos inoculated with both influenza A virus and the X strain of canine distemper virus were carried out in order that any active immunity following its administration could be assessed directly under naturally occurring conditions. Volunteers selected at random from the inmate populations of a number of State institutions were given a single subcut. injn. of complex vaccine of good antigenic potency 4 months before an outbreak of influenza. The incidence of influenza A during the epidemic was found to be 50% lower than among unvaccinated individuals in identical environmental circumstances. The results indicate that a vaccine which significantly increased antibodies against influenza A virus also significantly reduced the incidence of influenza A. Since the vaccine contained inactivated virus, it seems probable that its action was comparable to that of an inert antigen and that it served only to stimulate the production of anti-bodies and did not alter other factors which may possibly contribute to a state of relative immunity to influenza A. It is likely that the increased immunity observed was directly attributable to the increased antibody levels possessed by vaccinated individuals. The incidence of influenza of unknown cause was not significantly different in the 2 groups.