Update on Vaccine-Derived Poliovirus Outbreaks - Democratic Republic of the Congo and Horn of Africa, 2017-2018

Abstract

Widespread use of live attenuated (Sabin) oral poliovirus vaccine (OPV) has resulted in marked progress toward global poliomyelitis eradication (1). However, in underimmunized populations, extensive person-to-person transmission of Sabin poliovirus can result in genetic reversion to neurovirulence and paralytic vaccine-derived poliovirus (VDPV) disease (1). This report updates (as of February 26, 2019) previous reports on circulating VDPV type 2 (cVDPV2) outbreaks during 2017-2018 in the Democratic Republic of the Congo (DRC) and in Somalia, which experienced a concurrent cVDPV type 3 (cVDPV3) outbreak* (2,3). In DRC, 42 cases have been reported in four cVDPV2 outbreaks; paralysis onset in the most recent case was October 7, 2018 (2). Challenges to interrupting transmission have included delays in outbreak-response supplementary immunization activities (SIAs) and difficulty reaching children in all areas. In Somalia, cVDPV2 and cVDPV3 were detected in sewage before the detection of paralytic cases (3). Twelve type 2 and type 3 cVDPV cases have been confirmed; the most recent paralysis onset dates were September 2 (cVDPV2) and September 7, 2018 (cVDPV3). The primary challenge to interrupting transmission is the residence of >300,000 children in areas that are inaccessible for vaccination activities. For both countries, longer periods of surveillance are needed before interruption of cVDPV transmission can be inferred.

FIGURE 1

Circulating vaccine-derived poliovirus type 2 (cVDPV2) cases, by location and number of response supplementary immunization activities (SIAs) with monovalent oral poliovirus vaccine type 2 (mOPV2) — Democratic Republic of Congo, 2017–2018 * Each dot represents one confirmed paralytic cVDPV2 case. Dots are randomly positioned within health zones and do not represent exact locations where cases occurred.

FIGURE 2

Circulating vaccine-derived poliovirus (cVDPV) type 2 and type 3 cases, as of February 26, 2019, by location — Somalia, 2018 * Each symbol represents one confirmed paralytic cVDPV case. Symbols are randomly positioned within districts and do not represent exact locations where cases occurred.

FIGURE 3

Circulating vaccine-derived poliovirus (cVDPV) cases and outbreak response supplementary immunization activities, by month — Somalia, 2017–2018 Abbreviations: bOPV = bivalent oral poliovirus vaccine, types 1 and 3; cVDPV2 = circulating vaccine derived poliovirus type 2; cVDPV3 = circulating vaccine derived poliovirus type 3; mOPV2 = monovalent oral poliovirus vaccine type 2.