Evaluation of Sabin Live Poliovirus Vaccine in Japan Ii. Clinical, Virologic and Immunologic Effects of Vaccine in Children

Monovalent vaccine was fed to about 3, 000 children in the order of types 1, 3, 2 at 4week intervals. The results obtained confirm the effectiveness and the safety of the vaccine. Vaccinees demonstrated excellent antibody response to each type of vaccine. Heterotypic antibody response was shown in some vaccinees. Vaccine viruses readily spread to children coming in contact with vaccinees, resulting in a high incidence of seroconversion almost comparable to that obtained among vaccinees, although the viruses spread more readily among children in nurseries than among home dwelling children. None of the vaccinees developed any serious illness and no evidence was found to prove that any of the symptoms observed in some vaccinees was attributable to the vaccine virus. Clinical observation of the contacts gave no evidence for untoward clinical reaction. Vaccine viruses were readily isolated from stools of the vaccinees and contacts for several weeks. Concurrent infection of the intestinal tract with non-polio enteroviruses was shown to exert significant inhibitory effect on infection of the vaccine viruses and hence on antibody response. Pre-existing antibodies, heterotypic or homotypic, reduced the rate of virus excretion after vaccination, but did not significantly affect antibody response.