trivalent oral poliovirus vaccine

The trivalent oral poliovirus vaccine (tOPV) is a preparation of live, attenuated (weakened) poliovirus that contains all three serotypes of the virus: PV1, PV2, and PV3. Administered orally, it stimulates both systemic and local immune responses in the small intestine and lymph nodes, generating antibodies against wild poliovirus. This vaccine became predominant after its introduction in the early 1960s and is typically given in multiple doses to ensure near-complete immunity. While effective, tOPV can rarely lead to vaccine-derived polioviruses (VDPVs) or vaccine-associated paralytic polio (VAPP). Due to these risks, some countries have transitioned to inactivated poliovirus vaccine (IPV), though OPV may still be used strategically to enhance herd immunity in areas with ongoing transmission.12