Vaccination policies to prevent poliomyelitis in the United States have changed from an all-oral poliovirus vaccine (OPV) regimen, which began in 1961; to a sequential inactivated poliovirus (IPV)-OPV regimen, which was recommended in 1997; and most recently to an all-IPV regimen in 2000. These changes were prompted by the replacement of poliomyelitis due to wild-type poliovirus with vaccine virus-associated poliomyelitis (VAAP). Alexander and colleagues (2004) report on the effects of changes in vaccination policy on VAAP since 1990. From 1990 to 1996, 48 cases of poliomyelitis occurred in the United States; 2 cases were classified as possibly due to wild-type virus, and 46 were classified as VAAP. With the change in vaccination policy, 13 cases of poliomyelitis were reported from 1997 to 1999, and all were due to all-OPV regimens. Since 1999, there have been no cases of VAAP in the United States. In view of the continued possibility of poliovirus importation, of the reversion of vaccine-derived poliovirus to a more neurovirulent phenotype, and of laboratory-acquired infection, vaccination with IPV will need to continue in the United States.
Alexander LN et al: Vaccine policy changes and epidemiology of poliomyelitis in the United States. JAMA 293:1696, 2004