OPV is made with attenuated (weakened) polioviruses. On extremely rare occasions, the vaccine can
cause cases of vaccine-associated paralytic polio (VAPP) and circulating vaccine-derived polioviruses
(cVDPVs). To prevent cVDPVs and VAPP, OPV must be withdrawn as soon as possible after the end of
wild poliovirus (WPV) transmission.
tOPV contains all three poliovirus serotypes (1, 2 and 3), and the use of this vaccine has led to the
successful eradication of wild poliovirus type 2 (WPV2), with the last case occurring in 1999. Today,
over 90% of cVDPV cases, and approximately 40% of VAPP cases are due to the type 2 component of
tOPV.