Poliomyelitis; effect of Salk vaccine on severity of paralysis.

The severity of paralysis in 642 nonvaccinated patients with poliomyelitis and in 93 vaccinated patients was observed at the Los Angeles County General Hospital in 1956. In the vaccinated group of patients the proportion of nonparalytic and mild paralytic cases was consistently greater in each 5-year age group under age 15 than in the nonvaccinated. In the entire 0 to 14 age bracket, 12 per cent of the vaccinated patients had moderate or marked degrees of paralysis as compared to nearly 50 per cent of the nonvaccinated cases. There were too few vaccinated patients for comparison over this age. In the vaccinated group as a whole there was no apparent difference in severity as between patients who had had one inoculation and those who had had two. Among the small number of vaccinated patients under age 5, however, there was a suggestive decrease in severity between patients with one and with two inoculations. In nonvaccinated patients, the disease tended to be most severe in the 0 to 4 age group and young adults, ages 20 to 35. The largest number of deaths and of cases in which a respirator was needed occurred among young adults. None of the vaccinated patients died or needed a respirator, but tracheotomy was necessary for three. The concentration of mild cases in the vaccinated group is believed to indicate that partial protection was conferred by the vaccine, resulting in a shift to lesser degrees of severity. Such a shift would obscure the conversion of nonparalytic cases to inapparent infections. Convalescent follow-up examinations of 62 vaccinated and 68 nonvaccinated patients mostly in the 5 to 9 age group, revealed that in both series of patients approximately 90 per cent of the muscle groups graded as having "slight paralysis" at the time of discharge, were nonparalytic on the later examination.