The Influence of Natural and Artificially Induced Immunity on Alimentary Infections with Polioviruses

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Abstract
From mid-1953 through August, 1957, 117 episodes of household infections with polioviruses were observed among a study group consisting of between 157 and 118 representative households. Vaccination was begun in January, 1956 with a 2-dose course of Salk vaccine, and was completed in December, 1956 when a booster dose was given. De novo development of antibody induced by the vaccine was excellent in children possessing 1 or 2 types of heterologous antibody but among triple negatives nearly a quarter and a half, respectively, developed no antibody after the booster to types 1 and 3 viruses. Infection episodes continued at unreduced frequency in 1956 after the primary course but declined sharply in 1957 after the booster dose. However, analysis of the data as to intra-household infections suggests that this decline was not due to the vaccine. Measurable resistance to infection on intra-household exposure and reduced duration of viral excretion when infection did occur were observed among persons with natural homologous immunity. In contrast, among persons without natural immunity, vaccination apparently exerted no influence on susceptibility to, or the course of, alimentary infection. Resistance to homologous reinfection among the naturally immune was possibly related to homologous antibody titer but did not differ significantly in relation to viral type. Infected but vaccinated children appeared to be just as effective sources for intra-household spread of virus as did unvaccinated children, whereas some evidence was obtained that infected but naturally immune children are ineffective sources. A delay of at least 3 months in viral spread in one episode is believed to be strong evidence against spread from a pharyngeal source. Because of the foregoing evidence and the observations of other workers, including challenge experiments with live attenuated polioviruses; it is concluded that widespread use of Salk vaccine should not by any reasonable mechanism influence poliovirus dissemination.