Which statement about the switch from trivalent OPV to bivalent OPV and the introduction of IPV is incorrect?

• A. It removed the type 2 component to reduce VDPV2 outbreaks.
• B. It preserved immunity to PV1 and PV3.
• C. IPV provides systemic immunity.
• D. It increased risk of VDPV2 outbreaks.

Answer: (D)

The main idea is understanding how removing the type 2 component from the oral vaccine and adding an inactivated vaccine changes the risk of vaccine-derived type 2 poliovirus. Removing the type 2 component from OPV eliminates the live-type 2 strain from routine vaccination, which is the primary source of vaccine-derived type 2 outbreaks. By not using OPV2, opportunities for type 2 vaccine-derived viruses to circulate and mutate are greatly reduced. The switch maintains protection against types 1 and 3 because the new oral vaccine still covers those serotypes, so immunity to PV1 and PV3 remains. Introducing IPV provides systemic immunity by producing neutralizing antibodies in the blood, protecting individuals from paralytic disease should exposure occur, even though IPV doesn’t generate as strong mucosal immunity as OPV. Put together, this strategy targets reducing VDPV2 risk rather than increasing it. If any VDPV2 issues arise after the switch, they’re linked to immunity gaps or residual circulation from before the change, not the switch itself.