Which factor contributed to the decision to switch from OPV to IPV in the United States?

• A. To eliminate VAPP and due to decreasing risk of wild-type poliovirus importation.
• B. To maintain OPV usage.
• C. To reduce cold chain requirements.
• D. To enhance mucosal immunity.

Answer: (A)

Switching from OPV to IPV in the United States was driven by safety concerns tied to the live oral vaccine. OPV can, in rare cases, cause vaccine-associated paralytic polio and, if poliovirus circulation occurs, potentially evolve into a vaccine-derived poliovirus. By the time the U.S. made the switch, wild-type poliovirus transmission had been stopped for many years and the risk of importation was low. With high vaccination coverage and surveillance, IPV could provide solid protection against paralysis without the small risk of VAPP or VDPV, making it the safer choice. The other ideas don’t fit: maintaining OPV would keep VAPP risk; reducing cold chain needs isn’t the main driver and isn’t accurate for IPV; and mucosal immunity is stronger with OPV, not IPV.