Eradication of poliomyelitis in the United States. II. Experience with killed poliovirus vaccine.

Killed poliovirus vaccine was the only poliomyelitis vaccine available in the United States from 1954 to 1962. During that time, the incidence of poliomyelitis among non-vaccinated individuals decreased by 90%, an indication that the circulation of wild poliovirus had been reduced ("herd effect"). The rate of decline of wild poliovirus disease, which resulted from use of killed vaccine, did not change after oral, live poliovirus vaccine was introduced in 1962. Neither mass immunization campaigns nor use of an orally administered vaccine has increased rates of poliomyelitis immunization. Outbreaks of poliomyelitis can occur in susceptible subgroups in otherwise well vaccinated populations; therefore, the degree of population protection is best evaluated in terms of the number of susceptible individuals and their opportunities for contact with each other rather than in terms of the percentage of the total population vaccinated. Eradication of poliomyelitis and elimination of poliovirus from large populations are possible with use of killed poliovirus vaccine.