Basic conditions for the eradication of poliomyelitis--indications for a common prescription.

The efforts of the last decade to achieve the world eradication of poliomyelitis have resulted in several problems of methodology and field implementation of the polio control program: (1) The concept of eradication. Its present definition refers to the complete absence of activity of the wild poliovirus. It is the result of the decision to recommend the use of OPV for the world control of polio and leaves unanswered the problem of the paralytic disease associated with OPV. (2) Besides a successful vaccination policy the control of polio implies a satisfactory environment. Risk factors in the environment mean persistence of endemicity and reoccurrence of disease, even after several years of absence of polio activity. (3) Concerning the limitations of the two available vaccines, problems of immunogenicity, safety, and thermostability are associated with OPV. Use of EIPV requires a high coverage of all the ages at risk of infection, and gut immunity is lower than that induced by OPV. On the other hand, several observations point to the limitation of OPV to prevent the spread of the wild virus into the vaccinated community, as claimed for EIPV. Limitations of OPV are mainly vaccine associated paralytic disease in the developed countries, and wild virus associated disease in "vaccinated" individuals in the developing countries. Disease associated with EIPV programs is observed practically only in nonvaccinated individuals. EIPV, particularly if associated with OPV, offers a clear advantage over OPV alone, in terms of immunogenicity, safety, and protective efficacy. (4) Total elimination of paralytic poliomyelitis can hardly be conceived of without the use of the EIPV.