Update on Vaccine-Derived Polioviruses — Worldwide, January 2017–June 2018

Jaume Jorba, PhD; Ousmane M. Diop, PhD; Jane Iber, MSc; Elizabeth Henderson; Kun Zhao, PhD; Roland W. Sutter, MD; Steven G.F. Wassilak, MD; Cara C. Burns, PhD

Disclosures

Morbidity and Mortality Weekly Report. 2018;67(42):1189-1194. 

In This Article

Abstract and Introduction

Introduction

Since the Global Polio Eradication Initiative was launched in 1988,[1] the number of polio cases worldwide has declined by >99.99%. Among the three wild poliovirus (WPV) serotypes, only type 1 (WPV1) has been detected since 2012. This decline is attributable primarily to use of the live, attenuated oral poliovirus vaccine (OPV) in national routine immunization schedules and mass vaccination campaigns. The success and safety record of OPV use is offset by the rare emergence of genetically divergent vaccine-derived polioviruses (VDPVs), whose genetic drift from the parental OPV strains indicates prolonged replication or circulation.[2] Circulating VDPVs (cVDPVs) can emerge in areas with low immunization coverage and can cause outbreaks of paralytic polio. In addition, immunodeficiency-associated VDPVs (iVDPVs) can emerge in persons with primary immunodeficiencies and can replicate and be excreted for years. This report presents data on VDPVs detected during January 2017–June 2018 and updates previous VDPV summaries.[3] During this reporting period, new cVDPV outbreaks were detected in five countries. Fourteen newly identified persons in nine countries were found to excrete iVDPVs. Ambiguous VDPVs (aVDPVs), isolates that cannot be classified definitively, were found among immunocompetent persons and environmental samples in seven countries.

Global eradication of type 2 WPV (WPV2) was declared in 2015; type 3 WPV (WPV3) was last detected in 2012. The number of detected WPV1 cases has reached a historic low (22 cases in 2017 and 18 as of September 2018) in two of the three countries with endemic WPV1 transmission (Afghanistan and Pakistan); in Nigeria, WPV1 was last detected in September 2016. After the emergence of multiple cVDPV2 outbreaks during the preceding 15 years, in April 2016, all OPV-using countries switched from using trivalent OPV (tOPV; Sabin types 1, 2, and 3) to bivalent OPV (bOPV; Sabin types 1 and 3). To control and prevent cVDPV2 outbreaks, approximately 100 million doses of monovalent type 2 OPV (mOPV2) have been distributed in 11 countries.[4] To maintain protection from poliovirus type 2 paralysis, 176 OPV-using countries have introduced at least 1 dose of injectable inactivated polio vaccine beginning in 2015.

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