The oral polio vaccine (OPV) was developed in 1961 by Albert Sabin. Also called “trivalent oral polio vaccine” or “Sabin vaccine”, OPV consists of a mixture of live, attenuated (weakened) poliovirus strains of all three poliovirus types.
OPV produces antibodies in the blood to all three types of poliovirus. In the event of infection, these antibodies protect against paralysis by preventing the spread of wild poliovirus to the nervous system.
OPV also produces a local, mucosal immune response in the mucous membrane of the intestines. In the event of infection, these mucosal antibodies limit the replication of the wild poliovirus inside the intestine. This intestinal immune response to OPV is thought to be the main reason why mass campaigns with OPV can rapidly stop person-to-person transmission of wild poliovirus.
Source: http://www.polioeradication.org/Polioandprevention/Thevaccines/Oralpoliovaccine(OPV).aspx
