Abstract
Data on the incidence of paralytic poliomyelitis in relation to the vaccination status of the population suggest that the use of a killed poliovirus vaccine through the end of 1961 effected a reduction in the level of reported disease in unvaccinated, as well as vaccinated, persons. These data tend to substantiate belief of Bodian, Marine, and others that less than complete coverage of the population with the killed poliovirus vaccine has limited dissemination of poliovirus in the community. Part of the sharp downward trend, however, appears to have been caused by the changing socioeconomic composition of the unvaccinated population.