Update on Vaccine-Derived Poliovirus Outbreaks — Worldwide, July 2019–February 2020

Mary M. Alleman, PhD; Jaume Jorba, PhD; Sharon A. Greene, PhD; Ousmane M. Diop, PhD; Jane Iber, MSc; Graham Tallis, MBBS; Ajay Goel, MSc; Eric Wiesen, MS; Steven G.F. Wassilak, MD; Cara C. Burns, PhD


Morbidity and Mortality Weekly Report. 2020;69(16):489-495. 

In This Article

Abstract and Introduction


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 during July 2019–February 2020, 31 (94%) were cVDPV2; 18 (58%) of these followed new emergences. In mid-2020, the Global Polio Eradication Initiative (GPEI) plans to introduce a genetically stabilized, novel OPV type 2 (nOPV2) that has a lower risk for generating VDPV2 than does Sabin mOPV2; if nOPV2 is successful in limiting new VDPV2 emergences, GPEI foresees the replacement of Sabin mOPV2 with nOPV2 for cVDPV2 outbreak responses during 2021.[2,4,6]

*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.
Data as of March 25, 2020, for all emergences except ETH-ORO-1, ETH-ORO-2, ETH-ORO-3, ETH-SOM-1, and SOM-BAN-1, (as of March 24, 2020) and CHA-NDJ-1, NIE-JIS-1, NIE-KGS-1, NIE-KGS-2, NIE-SOS-6, and TOG-SAV-1 (as of March 27, 2020).