Analysis of a Sabin-Strain Inactivated Poliovirus Vaccine Response to a Circulating Type 2 Vaccine-Derived Poliovirus Event in Sichuan Province, China 2019-2021.

Importance: The Sabin-strain inactivated poliovirus vaccine (IPV) may be a tool for polio outbreak response in certain situations. Objective: To investigate the response to a type 2 vaccine-derived poliovirus (VDPV2) outbreak. Design, Setting, and Participants: This case series was conducted in China after a VDPV2 was detected in stool specimens from a child with acute flaccid paralysis (AFP) in Sichuan Province in 2019, 3 years after the global withdrawal of live, attenuated type 2 oral poliovirus vaccine (OPV). Investigation followed National Health Commission and World Health Organization guidance and included searching hospitals for unreported AFP cases; testing stool specimens from the child, his contacts, and local children; enhanced environmental surveillance for VDPV2s in wastewater; and measuring vaccination coverage. Sabin-strain IPV campaigns were conducted in a wide geographic area. Main Outcomes and Measures: Any VDPV2 detection after completion of the supplementary immunization activities. Results: A 28-nucleotide-change VDPV2 was isolated from a young boy. Three VDPV2s were detected in healthy children; 2 were contacts of the original child, and none had paralysis. A search of 31 million hospital records found 10 unreported AFP cases; none were polio. No type 2 polioviruses were found in wastewater. Prior to the event, polio vaccine coverage was 65% among children younger than 5 years. Sabin-strain IPV campaigns reached more than 97% of targeted children, administering 1.4 million doses. No transmission source was identified. More than 1 year of enhanced poliovirus environmental and AFP surveillance detected no additional VDPVs. Conclusions and Relevance: These findings suggest that the circulating VPDV2 outbreak in 2019 was associated with low vaccine coverage. An investigation discovered 3 infected but otherwise healthy children and no evidence of the virus in wastewater. Following Sabin-strain IPV-only campaigns expanding from county to prefecture, the poliovirus was not detected, and the outbreak response was considered by an expert panel and the World Health Organization to have been successful. This success suggests that the Sabin-strain IPV may be a useful tool for responding to circulating VDPV2 outbreaks when high-quality supplementary immunization activities can be conducted and carefully monitored in settings with good sanitation.

Detection and Initial Response to a Type 2 Vaccine-Derived Poliovirus - Sichuan Province, China, 2019.

WHAT IS ALREADY KNOWN ABOUT THIS TOPIC?: After the type 2 strain of the live, attenuated poliovirus vaccine was withdrawn globally in 2016, any identification of a type 2 poliovirus is a Public Health Emergency of International Concern. A vaccine-derived type 2 poliovirus (VDPV2) was identified in Sichuan, prompting an urgent, comprehensive investigation and response. WHAT IS ADDED BY THIS REPORT?: Type 2 monovalent, live, attenuated oral poliovirus vaccine (mOPV2) is being used to respond to the numerous VDPV2 outbreaks seen around the world. In contrast, the response in Sichuan used Sabin strain inactivated poliovirus (sIPV) to stop circulation of the VDPV2. In the 6 months following the vaccination response, there have been no VDPV2s detected in Sichuan, despite extensive search. WHAT ARE THE IMPLICATIONS FOR PUBLIC HEALTH PRACTICES?: Further search for the VDPV2 must continue in order to determine whether transmission has been stopped. The ongoing investigation and response to the Sichuan VDPV2 is providing evidence to the Global Polio Eradication Initiative on managing VDPV2 outbreaks.