Monovalent and trivalent poliovirus vaccines contain live attenuated Sabin strains of poliovirus for administration by the oral route. The term "poliovirus" distinguishes these vaccines from the formaldehyde-inactivated Salk type (Poliomyelitis Vaccine, U.S.P.). Both the live and inactivated vaccines provide protection against paralytic strains of poliovirus by stimulating the production of type-specific serum antibodies. In addition, the live poliovirus vaccine strains induce localized, type-specific intestinal resistance to reinfection with the virus. The relative effectiveness of monovalent live poliovirus vaccine, trivalent live poliovirus vaccine, and inactivated poliomyelitis vaccine has not been established with certainty.