Updated Characterization of Post-OPV Cessation Risks: Lessons from 2019 Serotype 2 Outbreaks and Implications for the...

Area of Science:

• Virology
• Epidemiology
• Public Health

Background:

• Global coordinated cessation of oral poliovirus vaccine (OPV) continues, with serotype 2-containing OPV (OPV2) withdrawn in 2016.
• Remaining risks include undetected OPV transmission and potential reintroduction, highlighted by 2019 outbreaks.
• Monovalent OPV2 is still used for outbreak response in many countries.

Purpose of the Study:

• To review the 2019 epidemiological experience with poliovirus serotype 2 outbreaks.
• To propose a new risk factor for unexpected OPV introduction in global cessation modeling.
• To explore the implications for restarting preventive OPV2 use in OPV-using countries.

Main Methods:

• Review of 2019 epidemiological data on poliovirus serotype 2 outbreaks.
• Development of an updated model for global poliovirus transmission and OPV evolution.
• Simulation analysis with and without the newly proposed risk of unexpected OPV introduction.

Main Results:

• Without the new risk, simulations indicate an 81% probability of needing to restart OPV2 use.
• Including the new risk of unexpected OPV introduction increases the probability of OPV2 restart to 89%.
• Contingency planning necessitates bulk production of OPV2, including genetically stabilized strains.

Conclusions:

• The polio endgame requires careful management of residual risks, including potential OPV2 reintroduction.
• Modeling suggests a high likelihood of needing to resume preventive OPV2 use to achieve eradication.
• Proactive measures, such as OPV2 production, are crucial for global polio eradication strategy.