This report is concerned with the production of subclinical poliomyelitis in the chimpanzee, and immunity to such infection. Subclinical infection was produced in eight chimpanzees by the administration of virus orally or intracutaneously, and was measured by the production of a virus carrier state and the development of neutralizing antibodies. Immunity was tested by attempting to induce the carrier state again by a challenge dose of virus by the same routes.

With an homologous strain as the challenge virus, immunity as defined here was produced in each of four chimpanzees tested. Neutralizing antibodies to the homologous strain were present about 1 month following the first exposure to virus by either the oral or cutaneous route.

In another group of two chimpanzees, one developed neutralizing antibodies and immunity to heterologous strains, and one did not.

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