The relation between acute persisting spinal paralysis and poliomyelitis vaccine--results of a ten-year enquiry. WHO Consultative Group.

Most of the 13 countries that participated in this ten-year study of the incidence of acute persisting spinal paralysis (APSP) used trivalent live poliomyelitis vaccine (Sabin strains), but monovalent vaccines were used for all or part of the time in 3 countries and inactivated vaccines were used wholly by 2 countries and in part by 2 other countries. Altogether 698 cases of APSP were recorded in a total population of about 509 million over the 10-year study period - an incidence of 0.14 per million per annum. The incidence varied widely between countries and not all the cases were related to immunization. In six countries where live vaccines were used three methods of assessment of risk were employed. The risk in relation to the child population under 3 years of age was less than 1 per million children in all six countries.In both vaccinees and contacts most cases were due to poliovirus type 3; of those due to type 2, the proportion was greater among contacts than among recipients. Since the results make it clear that neurovirulence tests for safety do not prove the innocuity of a vaccine with absolute certainty, it is essential that every programme of poliomyelitis immunization should include a continuous and effective system of surveillance. The study showed the need for the immunization of presumed susceptible adults at the same time as their children are vaccinated.Though in most countries the incidence of vaccine-associated cases was low, two countries had much higher rates. In one the rate has now fallen but in the other it persists at the same level as before. No clear explanation of the differences between these and the other countries was obtained.