Outbreaks of Circulating Vaccine-Derived Poliovirus in the World Health Organization Western Pacific Region, 2000-2021.

The World Health Organization Western Pacific Region (WPR) has maintained a polio-free status for more than two decades. At the global level, there were only six confirmed polio cases due to wild type 1 poliovirus in Pakistan, Afghanistan, and Malawi in 2021; therefore, the risk of wild poliovirus importation from endemic countries to the WPR is considerably lower than that in the past. However, the risk of polio outbreaks associated with circulating vaccine-derived polioviruses (cVDPVs) cannot be ignored even in the WPR. Since the late 2010s, cVDPV outbreaks in the WPR have increased in frequency and magnitude. Moreover, the emergence of concomitant polio outbreaks of type 1 and type 2 cVDPVs in the Philippines and Malaysia during 2019-2020 highlighted the potential risk of cVDPV outbreaks in high-risk areas and/or communities in the WPR. Previous cVDPV outbreaks in the WPR have been rapidly and effectively controlled. However, future polio outbreak risks associated with cVDPVs must be reconsidered, and polio immunization and surveillance strategies should be updated accordingly.