Poliomyelitis

In 1955 the Salk inactivated polio vaccine was introduced. It was followed by the Sabin live, attenuated oral vaccine in 1961. These two vaccines have made it possible to eliminate polio on a global level.

The Salk vaccine as it has been presently developed produces a high level of immunity after two or three injections with only minor side-effects. The major defense the Salk vaccine provides against polio viruses is to prevent them from spreading from the digestive system to the nervous system and respiratory system. But it cannot prevent the viruses from entering the intestinal tract. The Salk vaccine has been effective in certain countries, like those in Scandinavia and the Netherlands, where children received a minimum of six shots before reaching the age of 15. Those countries have good sanitation and the major form of spreading the viruses was through respiratory contagion.

In countries that do not have good sanitation, the Sabin vaccine is preferred because as an oral vaccination it is goes straight to the intestinal tract and builds up immunity there as well as in other parts of the body. Those who have received the vaccine may pass on vaccine viruses through the feces to non-vaccinated members of the population, and that spreads the good effects of immunization. There is, however, the rare adverse side-effect of 1 out of 2,500,000 doses of the Sabin vaccine producing a case of poliomyelitis.

The number of doses to achieve a high level of immunity for the Sabin oral vaccine in temperate, economically advanced countries may be two or three. In tropical countries the degree of immunization is not as high against all three types of polio viruses. The effectiveness of the Sabin oral vaccine in tropical countries is improved when it is administered in the cool and dry seasons and when it is given as part of mass campaign where there is a chance of vaccinated persons passing the vaccine virus on to non-vaccinated persons.

Toward the global eradication of polio, the World Health Organization recommends the Sabin oral vaccine for its better performance in creating overall polio immunity, its convenient form of administration, and for its lower cost.