SHEDDING OF VIRULENT POLIOVIRUS REVERTANTS DURING IMMUNIZATION WITH ORAL POLIOVIRUS VACCINE AFTER PRIOR IMMUNIZATION WITH INACTIVATED POLIOVACCINE

Fecal shedding of virulent revertant polioviruses was examined in isol ates from infants previously immunized with greater-than-or-equal-to 1 dose of orally administered live attenuated polio vaccine (OPV) alone , enhanced-potency inactivated polio vaccine (EIPV) alone, or a combin ation of both. After administration of OPV alone, vaccine poliovirus s erotypes were recovered in feces within 1 week and for as long as 31-6 0 days in 30%-80% of subjects after 1 or 2 doses and in 30%-50% after immunization with greater-than-or-equal-to 3 doses. No revertant polio virus shedding was observed after OPV challenge in subjects immunized previously with greater-than-or-equal-to 3 doses of OPV. However, feca l shedding of revertant poliovirus after OPV challenge was observed in 50%-100% of subjects previously immunized with greater-than-or-equal- to 3 doses of the EIPV. These findings suggest that prior immunization with EIPV does not prevent fecal shedding of revertant polioviruses a fter subsequent reexposure to OPV.