Strategies for poliomyelitis eradication in developing countries.

Oral polio vaccine (OPV) delivered only through routine services does not appear to interrupt wild virus transmission in the developing countries. The experience in the Americas, which despite intensive surveillance has not confirmed any cases of paralytic poliomyelitis due to wild poliovirus since 23 August 1991, has shown the necessity of delivery of additional doses of OPV through mass campaigns targeted at all children under five years of age regardless of their previous immunization status and in special mop-up operations targeted at this same age group in areas categorized as at high risk of virus transmission, such as those that harbored the virus in the recent past. High-risk areas were determined by empirical observations, which were subsequently confirmed by molecular epidemiology which indicated the presence of several "reservoirs" that helped maintain transmission over several years. During mop-ups, OPV is delivered house by house. This paper discusses the rationale for the utilization of these strategies and outlines the phases for their preparation and evaluation, with illustrations from recent experiences with the last cases of paralytic poliomyelitis in the Americas.