When and why did the global switch from trivalent OPV to bivalent OPV occur?

• A. In 2016, to remove type 2 strain after eradication of WPV2 and reduce cVDPV2 risk.
• B. In 2012, due to supply shortages.
• C. In 2020, to align with new vaccine development.
• D. In 1998, to reduce production costs.

Answer: (A)

The main idea is to reduce the risk from vaccine-derived poliovirus by removing the type 2 component of the oral vaccine once type 2 wild poliovirus had been eradicated. In 2016, countries worldwide switched from trivalent OPV (covering types 1, 2, and 3) to bivalent OPV (types 1 and 3). This eliminated the live type 2 strain from routine vaccination, lowering the chance that the attenuated type 2 virus could revert and cause circulating vaccine-derived poliovirus type 2 outbreaks. To keep protection against types 1 and 3, bOPV is used, and many places added IPV to maintain immunity to type 2 without the risks tied to a live vaccine strain. The other dates and reasons don’t match the eradication timeline or the rationale for reducing cVDPV2 risk.