THE PATTERN of occurrence of poliomyelitis in the United States has changed. In each succeeding year this change has become better defined. The disease is now concentrated among the unimmunized population, which we have failed to reach while we have all shared in the most intensive campaign of vaccination in the history of the United States. The residual pattern of disease represents a measure of our failure to apply vaccine completely enough. The following remarks will attempt to summarize briefly our present status. The data to be presented are largely those collected by the Poliomyelitis Surveillance Unit of the Communicable Disease Center.
Figure 1 shows the annual poliomyelitis incidence rates for the period 1935-1960. After the peak period 1950-54, a downward trend began in 1955 and was continued through 1957, associated with increasing use of Salk vaccine. Although this trend was halted and reversed in 1958 and 1959,