Both live, oral (Sabin) and killed, intramuscular (Salk) vaccines can be used to protect against polio. In South Africa the trivalent live oral polio vaccine is used. It has been weakened (attenuated) to give immunity (against all 3 strains of polio virus) without causing clinical infection. The killed vaccine is equally effective as the live vaccine. Only the oral vaccine is used in South Africa. It is hoped that universal immunisation will eradicate polio as has happened to smallpox.
Live (oral) attenuated polio vaccine was introduced in 1962. It is excreted in the stool and can infect others asymptomatically and thereby boost the immunity of the whole community. It is best used in communities where wild polio virus may still occur. With the elimination of clinical polio, the inactivated (intramuscular) Salk vaccine can be used instead as part of a single combination vaccine (e.g. DPT/ Hib/ inactivated polio). The Salk vaccine avoids the rare cases of oral polio vaccine induced paralysis.