Poliomyelitis Immunization

Abstract

I would summarize the foregoing discussion by asserting, first, that the superiority of the live oral attenuated poliovirus vaccines over the inactivated vaccines now in use remains to be demonstrated, except for convenience of administration. Second, the proposal to introduce live oral poliovirus vaccine by means of country-wide mass immunization programs is irresponsible in the sense that such a procedure would eliminate the possibility of a definitive evaluation of either vaccine in this country, and moreover is unlikely to accomplish more than can be accomplished by a more conservative approach. Third, even after licensing, a new vaccine product must be considered to be on trial, since new variables enter the scene when large-scale manufacture and large-scale use begin. In this connection it is of importance that the margin of safety of live-attenuated-poliovirus lots now in production is not large, as measured by the only laboratory test available—neurovirulence in monkeys. In comparison with unacceptable trial strains, about which questions of safety have been raised after field use, the acceptable strains have measurably less neurovirulence, but the differences are not great, and approval of each lot will require careful scrutiny for evidence of even slight degrees of reversion in neurovirulence during production. Finally, there is a place for both types of vaccine in the control of poliomyelitis throughout the world. How and where each type should be used is a scientific problem which can best be resolved with careful assessment of all the available evidence concerning vaccine characteristics in relation to the ecology of poliomyelitis. From the point of view of a scientific evaluation of the results of the present waccination program in this country, it appears that a quip I made in 1960 (13)—we may now have too many poliomyelitis vaccines!—has come home to roost.