Using inactivated poliovirus from all three serotypes, Jonas Salk developed the first vaccine for poliovirus in 1952. The inactivated poliovirus vaccine (IPV) was used in the United States until the early 1960ís when an oral poliovirus vaccine (OPV) containing live attenuated strains of poliovirus was developed. Use of OPV was discontinued in the US in 2000 and replaced with an enhanced-potency IPV. Introduction of the original vaccine resulted in a dramatic decline of global polio incidence and, within 20 years, the elimination of wild type poliovirus in the US. The last cases of poliomyelitis caused by endemic transmission of the wild type virus in the US were reported in 1979 in several Midwestern states. The last natural case of polio in the Western Hemisphere was in Peru in 1991, though occasional cases still crop up when virus in the oral vaccine reverts to a more virulent state.
Polio has not been completely eradicated in the world yet, but aggressive vaccination programs run by the World Health Organization (WHO) have done a remarkable job of reducing its prevalence. Today, vaccination efforts are focused mainly on India, Nigeria, Egypt, Pakistan, Afghanistan, Somalia and Niger, but poliovirus can easily be imported into polio-free countries where it spreads rapidly among unvaccinated individuals. For example, in 2003 when the first reported polio case in ten years appeared in Lebanon, DNA sequencing showed that the virus was most likely from India.