Vaccination against poliomyelitis

Effective immunization against poliomyelitis has been achieved with two different vaccines. An injectable killed, or inactivated, poliovirus vaccine was introduced in the mid-1950s, and an oral live, attenuated poliovirus vaccine was introduced in the late 1950s and early 1960s. In areas of the world where only the killed virus vaccine has been used, poliomyelitis has been brought fully under control; however, in areas where the live virus vaccine is in use, problems in the control of poliomyelitis continue to exist. Experience in recent years has revealed two particular difficulties related to the use of live, attenuated poliovirus vaccine: 1. The live virus vaccine is occasionally associated with paralytic disease, and in countries where paralytic poliomyelitis has been brought under control, it may be a more frequent cause of polio than the wild virus. The attenuated virus has been shown to revert to neurovirulence, and can reseed the natural virus reservoir, becoming established in a human population. This will be discussed in detail in the “Effect of Vaccination Programme” section. 2. In underdeveloped countries with warm climates, where poliomyelitis is still prevalent, antibody response to the live virus vaccine is uncertain because unexplained inhibitors in the intestinal tract interfere with vaccine virus implantation (Tables 1 and 2). In some countries four or more doses of the live virus vaccine have failed to protect against paralytic poliomyelitis. There are the separate problems of loss of vaccine potency due to the need to maintain the live vaccine in the frozen state, and its uncertain booster effect, even in temperate climates such as England86.