A change in the national polio vaccination policy has led to the elimination of vaccine-associated paralytic poliomyelitis

A change in the national polio vaccination policy has led to the elimination of vaccine-associated paralytic poliomyelitis (VAPP), according to a study in the October 13 issue of JAMA.

According to background information in the article, the last case of poliomyelitis (polio) in the United States caused by a naturally occurring virus occurred in 1979; however, as a consequence of oral poliovirus vaccine (OPV) use that began in 1961, an average of 9 cases of VAPP were confirmed each year from 1961 through 1989. To reduce the VAPP burden, national vaccination policy changed in 1997 from reliance on OPV to options for a schedule of inactivated poliovirus vaccine (IPV) followed by OPV. In 2000, an exclusive IPV schedule was adopted.

Lorraine Nino Alexander, M.P.H., of the Centers for Disease Control and Prevention, Atlanta, and colleagues reviewed national polio surveillance data in the United States from 1990 through 2003, examining the epidemiology of polio and assessing the association between the vaccine schedule changes and VAPP in the United States.

The researchers found that from 1990 through 1999, 61 cases of paralytic polio were reported; 59 (97 percent) of these were VAPP (1 case per 2.9 million OPV doses distributed), 1 case was imported, and 1 case was indeterminate. Thirteen cases occurred during the 1997-1999 transitional policy period and were associated with the all-OPV schedule; none occurred with the IPV-OPV schedule. No cases occurred after the U. S. implemented the all-IPV policy in 2000. The last imported polio case occurred in 1993 and the last case of VAPP occurred in 1999.

"Following this change, all forms of poliomyelitis have been eliminated in the United States...," the authors write. "The only threats from polio in the United States are from laboratories and the few remaining polio-endemic areas in Africa and Asia."

"Elimination of VAPP is an important public health accomplishment in the United States. However, it is crucial that the United States continues to maintain high vaccination coverage and a sensitive surveillance system to rapidly detect and respond to cases of suspected paralytic poliomyelitis, either from imported virus or from possible breaches in laboratory containment that could introduce laboratory strains. Poliovirus - from any source - that reaches communities with low vaccine coverage may result in endemic or epidemic transmission," the researchers conclude.

In an accompanying editorial, John F. Modlin, M.D., of the Dartmouth-Hitchcock Medical Center, Lebanon, N.H., writes on what needs to be done to keep polio from reappearing in the U.S.

"It is unlikely that a stockpile would need to be used as long as immunity levels can be maintained at the current high rates with routine IPV immunization of children. Overall polio vaccine coverage in the United States is now well above the approximately 80 percent level commonly associated with herd immunity, and evidence suggests that vaccination rates in inner cities are improving. However, some small risk will persist if virulent polioviruses are introduced into and allowed to spread within pockets of U.S. society where immunization is refused for religious or philosophical reasons or where access to immunization is hindered by low socioeconomic status.

"It is prudent to acquire a U.S. polio vaccine stockpile, despite the existing formidable barriers. At some currently unpredictable but comfortable period of time after the world is certified to be free of circulating virulent polioviruses, it will be possible to discontinue all poliovirus immunization," Dr. Modlin writes.