Risk Assessments for Type 1 Wild Poliovirus and Type 2 Vaccine-Derived Poliovirus Importation and Transmission -...

All countries face the potential threat of imported polioviruses, including both wild type and circulating vaccine-derived polioviruses. In response, we conducted a province-level assessment in China to evaluate the risk of importation and transmission of type 1 wild poliovirus (WPV1) and type 2 vaccine-derived poliovirus (VDPV2).

Distinct risk assessment tools for WPV1 and VDPV2 were employed, incorporating three primary indicators - population immunity, poliovirus surveillance, and importation risk. WPV1 was assessed using 13 secondary indicators, whereas VDPV2 utilized 21 secondary indicators. Assessments used comprehensive provincial data from the preceding five years. Scores (S-values) were derived from the secondary indicators' criteria and ratings, and used to classify the provincial-level administrative divisions (PLADs) into three risk categories: high, medium, and low. The top 10% of PLADs were designated as high-risk, with the remaining provinces equally distributed into medium- and low-risk categories.

In 2023, Xizang, Qinghai, and Xinjiang PLADs faced the highest risk of WPV1 importation and transmission; Xizang, Shaanxi, and Hainan PLADs were at the greatest risk for VDPV2 importation and transmission.

Risk assessment for VDPV2 importation and transmission has identified a distinct set of high-risk provinces compared to those identified by WPV1 risk assessment. Preventive and proactive response measures tailored to the specific risks should be implemented to maintain China's polio-free status.