Update on Vaccine-Derived Poliovirus Outbreaks — Worldwide, July 2019–February 2020
Mary Alleman, Jaume Jorba, Sharon A. Greene, Ousmane M. Diop, Jane Iber, Graham Tallis, Ajay Kumar Goel, Eric Wiesen, Steven G.F. Wassilak, Cara C. Burns
Abstract
Circulating vaccine-derived polioviruses (cVDPVs) can emerge in areas with low poliovirus immunity and cause outbreaks* of paralytic polio (1-5). Among the three types of wild poliovirus, type 2 was declared eradicated in 2015 (1,2). The use of trivalent oral poliovirus vaccine (tOPV; types 1, 2, and 3 Sabin strains) ceased in April 2016 via a 1-month-long, global synchronized switch to bivalent OPV (bOPV; types 1 and 3 Sabin strains) in immunization activities (1-4). Monovalent type 2 OPV (mOPV2; type 2 Sabin strain) is available for cVDPV type 2 (cVDPV2) outbreak response immunization (1-5). The number and geographic breadth of post-switch cVDPV2 outbreaks have exceeded forecasts that trended toward zero outbreaks 4 years after the switch and assumed rapid and effective control of any that occurred (4). New cVDPV2 outbreaks have been seeded by mOPV2 use, by both suboptimal mOPV2 coverage within response zones and recently mOPV2-vaccinated children or contacts traveling outside of response zones, where children born after the global switch are fully susceptible to poliovirus type 2 transmission (2-4). In addition, new emergences can develop by inadvertent exposure to Sabin OPV2-containing vaccine (i.e., residual response mOPV2 or tOPV) (4). This report updates the January 2018-June 2019 report with information on global cVDPV outbreaks during July 2019-February 2020 (as of March 25, 2020) (2). Among 33 cVDPV outbreaks reported * In this report, a cVDPV outbreak is defined as two or more independent isolations (through acute flaccid paralysis [AFP] or environmental surveillance or from a healthy community member following a confirmed AFP case) of genetically linked VDPVs. The number of outbreaks is equivalent to the number of cVDPV emergences. In summaries, a given cVDPV emergence/outbreak is counted once regardless of the number of countries affected following transmission beyond national borders.