Maximizing Polio Vaccine Efficacy

How long does immunity against polio last in a person vaccinated with oral poliovirus vaccine (OPV)? With inactivated poliovirus vaccine (IPV)?

---- William Morris, MD
Athens, Tenn

IPV was introduced in the United States in 1955; by 1963 it had been replaced by live, attenuated OPV. With universal immunization, both the incidence of paralytic poliomyelitis and the circulation of naturally occurring polioviruses had declined precipitously within a decade.¹ Thus, there was little opportunity to assess the long-term immunity induced by either IPV or OPV in the United States, and the situation in other developed countries has been similar.

Most authorities believe that successful immunization with either IPV or OPV results in long-term protection that probably persists for life. This conventional wisdom is supported by observations that poliomyelitis occurs very rarely in fully immunized persons in developed countries--and with no relationship to time from vaccination (ie, waning immunity has not been observed).

Polio vaccine efficacy is reduced by the absence of seroconversion in resource-poor settings where enteric viruses, such as rotavirus, interfere with OPV virus replication in the GI tract, or where high levels of maternal antibody reduce seroconversion to IPV when given in early infancy.^2-4 Indeed, primary OPV vaccine failure has become one of the major obstacles to eradicating poliomyelitis worldwide.

---- John F. Modlin, MD
Professor of Pediatrics and Medicine Chair, Department of Pediatrics
Dartmouth Medical School
Lebanon, NH