Global Outbreak Update: Circulating vaccine-derived poliovirus type 2 (cVDPV2)
Rising cases of circulating vaccine-derived poliovirus type 2 (cVDPV2) in parallel to the wild poliovirus type 1 (WPV1) variant. The African region, Afghanistan and Pakistan are particularly affected.
Update Date: 26 March 2021
Time frame and cases: In 2020, 959 human cases of circulating vaccine-derived poliovirus type 2 (cVDPV2) and 411 cVDPV2-positive environmental samples were reported from 27 countries. Of these, 21 countries were from the African Region (in Angola, Benin, Burkina Faso, Cameroon, Central African Republic, Chad, Côte d’Ivoire, Democratic Republic of the Congo, Ethiopia, Ghana, Guinea, Kenya, Liberia, Mali, Niger, Nigeria, Republic of Congo, Senegal, Sierra Leone, South Sudan and Togo) and 6 countries from the Eastern Mediterranean, Europe (Tajikistan) and the Western Pacific (Philippines and Malaysia). This followed a rising trend of cases compared to 2019.
Regions: As of March 2021, WHO risk assessments according to national reporting and regional monitoring, determines the following: 1. For the African region, the WHO considers a high risk of international spread and/or emergence of cVDPV2 due to the low population immunity against poliovirus type 2 (PV2), low IPV vaccination coverage, mass population movements, and strained national health services due to the COVID-19 pandemic. 2. For the Eastern Mediterranean (including Pakistan and Afghanistan), there is a high risk of international spread and/or emergence of cVDPV2 due to known polioviruses that have persisted over a year in certain populations, and the risk of population pockets without polio immunity, due to hard reach for vaccination campaigns. In the European and Western Pacific regions a moderate to low risk is determined.
Virus / Vector / Disease Information: Wild poliovirus type 1 (WPV1) and circulating vaccine-derived poliovirus type 2 (cVDPV2) are both circulating in the regions aforementioned.
Response: For the African Region, the response strategy based on international outbreak response guidelines, supported by the Regional Rapid Response Team. In Afghanistan, efforts focus on adapting vaccination campaign approaches to the current COVID-19 response. In Pakistan, polio vaccination was resumed amidst the COVID-19 situation, and given the dual threat of different strains, trivalent oral poliovirus vaccine (tOPV) was reintroduced as supplementary immunization activities (SIAs). In Tajikistan, local health authorities are preparing to fast-track response with nOPV2 campaigns.
Recommendations: The WHO recommends that countries, territories and areas should also maintain uniformly high routine immunization coverage at the district level to minimize the consequences of any new virus introduction. The WHO’s International Travel and Health recommends that all travellers to polio-affected areas be fully vaccinated against polio. Residents (and visitors for more than 4 weeks) from infected areas should receive an additional dose of OPV or IPV within 4 weeks to 12 months of travel.
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