What is the oral polio vaccine?

The oral polio vaccine, or OPV, was developed in the early 1960s and became a major tool in global polio control. It is easy to give, inexpensive, and can reduce transmission because it creates immunity in the intestines where poliovirus first multiplies. The vaccine was central to the dramatic decline in polio worldwide. In some settings, however, countries have shifted toward the inactivated injectable vaccine because of the rare risk of vaccine-derived poliovirus. Both vaccines have been important in the fight against polio.