Worst-case scenarios: Modeling uncontrolled type 2 polio transmission

Area of Science:

• Epidemiology
• Virology
• Public Health

Background:

• The Global Polio Eradication Initiative (GPEI) ceased most type 2 oral poliovirus vaccine (OPV2) use in 2016.
• Since then, over 3,000 paralytic polio cases caused by type 2 vaccine-derived polioviruses have been reported across 39 countries.
• Type 2 poliovirus transmission persists, posing risks of importation into high-transmission areas.

Purpose of the Study:

• To model the future trajectory of type 2 poliovirus transmission.
• To assess the probability of eradicating type 2 poliovirus with current and novel interventions.
• To identify strategies for avoiding catastrophic scenarios of polio expansion.

Main Methods:

• Utilized polio endgame modeling based on prior studies.
• Assessed current national and GPEI outbreak response performance.
• Evaluated the impact of novel type 2 oral poliovirus vaccine (nOPV2) under emergency use.

Main Results:

• Current strategies, even with nOPV2, show no probability of eradicating type 2 polioviruses in the near term.
• Worst-case scenarios predict rapid expansion of paralytic polio cases.
• Continued transmission risks high-consequence events and jeopardizes the goal of polio eradication.

Conclusions:

• Avoiding catastrophic polio scenarios requires developing strategies to significantly raise population immunity to type 2 polioviruses.
• The current approach to managing type 2 poliovirus is insufficient for eradication.
• Urgent development of new strategies is crucial to achieve the permanent end of poliomyelitis.