“Clearly, polio has been eradicated from the Americas, and tremendous progress has been made [globally]. . . . But we also must recognize that since 1988, the volume of both tourists and immigrants has grown in many categories exponentially. . . . Therefore, we have fewer reservoirs [of disease], but we have a lot more movement into and out of those reservoirs. . . . I would be willing to predict that we can see three to four documented importations over the next five years. . . . A change in the United States would have direct implications insofar as the other countries are concerned. It is my belief that the next three to five years are the truly critical ones. . . . At that point it will be far easier to take major decisions without particular implications in an international setting.”
From a presentation by D.A. Henderson in advocacy of an OPV vaccination strategy, CDC-sponsored polio vaccine workshop, June 8, 1995.
The major disadvantage of OPV is the occurrence of VAPP. Over the last 12 years in the United States, the incidence of VAPP has been about 8 to 10 cases per year. Some of those individuals may develop post-polio syndrome (a recurrence or worsening of symptoms, possibly including paralysis) in subsequent years, just as have many of those who contracted polio from the wild-type poliovirus. In this regard IPV has a major advantage: no cases of VAPP occur following its use.
Reversion of some bases of the virus to a more neurovirulent strain occurs after OPV vaccination with all three serotypes, but particularly serotype 3. These “revertant” viruses are not wild-type, and the virus recovered from patients with vaccine-associated cases of polio is not always a revertant. Other genetic changes in the virus are sometimes seen as well.
The risk of VAPP in immunodeficient children is 3,000 times that in normal children and occurs primarily in children with disorders of B-cell function, agammaglobulinemia, and Bruton's X-linked agammaglobulinemia. Vaccine-associated polio appears to be less frequent in developing countries, where OPV is given at an earlier age than in the United States. It is possible that maternal antibody may be protective against vaccine-associated polio. In addition, record-keeping in developing countries is often deficient, and there may be no means for distinguishing VAPP from wild-type polio disease.