An epidemic of poliomyelitis in southern Kerala.

An epidemic of poliomyelitis was recognized in May 1987 when there was a sharp increase in the number of children with acute paralytic poliomyelitis admitted to the SAT Hospital in Trivandrum in Kerala State. From May through September, 392 cases were admitted; the total admitted cases in 1987 were 458 in contrast to 119 in 1986. Evidence for type 1 poliovirus infection was found in 33 (85%) of the 39 children in whom virological investigations were done during the epidemic. In addition, evidence for poliovirus type 3 infection was found in four children. Data on the immunization status was available on 231 affected children in the epidemic; 175 (76%) had not received oral polio vaccine (OPV); 55 (24%) had received one or two doses and only one child had received three doses. Thus, lack of immunization was a major risk factor for disease. The estimated vaccine coverage with three doses of OPV in Kerala, based on the quantity of vaccine distributed during the years 1985, 1986 and 1987 were 94%, 100% and 91%, respectively. This outbreak occurred in spite of high vaccine coverage, and it illustrates the need for even higher coverage rates; the usefulness of hospitals as sentinel surveillance centres; the need for decentralized vaccine coverage data in order to prevent build-up of unimmunized susceptible children in any region; and the urgent need of a mechanism to respond to an epidemic quickly, with immunization, in order to curtail it.