Potential use of new poliomyelitis vaccines: memorandum from a WHO meeting.

Largely due to the intensive use of Sabin attenuated oral vaccines, the incidence of poliomyelitis is continuing to decline, particularly in the western hemisphere. In developing and tropical countries, use of trivalent attenuated vaccine may, however, sometimes produce suboptimal antibody responses, especially to type 1 and 3 polioviruses. Epidemics of poliomyelitis continue to occur in some countries with high vaccination coverage, though these are rare, and cases of vaccine-associated paralysis could become increasingly visible in countries that achieve control of the wild-type virus. Recent progress in understanding the biology of polioviruses has suggested several possible approaches to solving some of these problems. This Memorandum discusses the broad scientific and ethical criteria that would justify submitting new attenuated oral poliomyelitis vaccine candidates to different levels of testing in the laboratory and in humans.