Chukwuma Mbaeyi1, Thomas Moran2, Zubair Wadood2, Fazal Ather3, Emma Sykes4, Joanna Nikulin4, Mohammad Al Safadi2, Tasha Stehling-Ariza5, Laurel Zomahoun2, Abdelkarim Ismaili4, Nidal Abourshaid6, Humayun Asghar4, Gulay Korukluoglu7, Erwin Duizer8, Derek Ehrhardt5, Cara C Burns5, Magdi Sharaf4. 1. United States Centers for Disease Control and Prevention, 1600 Clifton Rd. NE, Atlanta, GA 30329, USA. Electronic address: cmbaeyi@cdc.gov. 2. World Health Organization Headquarters, Avenue Appia 20, 1202 Geneva, Switzerland. 3. Middle East and North Africa Office, United Nations Children's Fund, Abdulqader Al-Abed Street, Building No. 15, Tla'a Al-Ali, Amman, Jordan. 4. World Health Organization, Regional Office for the Eastern Mediterranean, Mohammad Jamjoum Street, Ministry of Interior Circle Building No. 5, P.O. Box 811547, Amman 11181, Jordan. 5. United States Centers for Disease Control and Prevention, 1600 Clifton Rd. NE, Atlanta, GA 30329, USA. 6. Syria Country Office, United Nations Children's Fund, East Mazzeh, Al Shafiee St., Damascus, Syria. 7. Public Health Institutions of Turkey, Adnan Saygun Cad. No. 55, F Blok 06100 Sihhiye, Ankara, Turkey. 8. National Polio Laboratory, Centre for Infectious Disease Control, National Institute for Public Health and the Environment, P.O. Box 1, 3720 BA, Bilthoven, the Netherlands.
Abstract
BACKGROUND: Outbreaks of circulating vaccine-derived polioviruses (cVDPVs) pose a threat to the eventual eradication of all polioviruses. In 2017, an outbreak of cVDPV type 2 (cVDPV2) occurred in the midst of a war in Syria. We describe vaccination-based risk factors for and the successful response to the outbreak. METHODS: We performed a descriptive analysis of cVDPV2 cases and key indicators of poliovirus surveillance and vaccination activities during 2016-2018. In the absence of reliable subnational coverage data, we used the caregiver-reported vaccination status of children with non-polio acute flaccid paralysis (AFP) as a proxy for vaccination coverage. We then estimated the relative odds of being unvaccinated against polio, comparing children in areas affected by the outbreak to children in other parts of Syria in order to establish the presence of poliovirus immunity gaps in outbreak affected areas. FINDINGS: A total of 74 cVDPV2 cases were reported, with paralysis onset ranging from 3 March to 21 September 2017. All but three cases were reported from Deir-ez-Zor governorate and 84% had received < 3 doses of oral poliovirus vaccine (OPV). After adjusting for age and sex, non-polio AFP case-patients aged 6-59 months in outbreak-affected areas had 2.5 (95% CI: 1.1-5.7) increased odds of being unvaccinated with OPV compared with non-polio AFP case-patients in the same age group in other parts of Syria. Three outbreak response rounds of monovalent OPV type 2 (mOPV2) vaccination were conducted, with governorate-level coverage mostly exceeding 80%. INTERPRETATION: Significant declines in both national and subnational polio vaccination coverage, precipitated by war and a humanitarian crisis, led to a cVDPV2 outbreak in Syria that was successfully contained following three rounds of mOPV2 vaccination. Published by Elsevier Ltd.
BACKGROUND: Outbreaks of circulating vaccine-derived polioviruses (cVDPVs) pose a threat to the eventual eradication of all polioviruses. In 2017, an outbreak of cVDPV type 2 (cVDPV2) occurred in the midst of a war in Syria. We describe vaccination-based risk factors for and the successful response to the outbreak. METHODS: We performed a descriptive analysis of cVDPV2 cases and key indicators of poliovirus surveillance and vaccination activities during 2016-2018. In the absence of reliable subnational coverage data, we used the caregiver-reported vaccination status of children with non-polio acute flaccid paralysis (AFP) as a proxy for vaccination coverage. We then estimated the relative odds of being unvaccinated against polio, comparing children in areas affected by the outbreak to children in other parts of Syria in order to establish the presence of poliovirus immunity gaps in outbreak affected areas. FINDINGS: A total of 74 cVDPV2 cases were reported, with paralysis onset ranging from 3 March to 21 September 2017. All but three cases were reported from Deir-ez-Zor governorate and 84% had received < 3 doses of oral poliovirus vaccine (OPV). After adjusting for age and sex, non-polio AFP case-patients aged 6-59 months in outbreak-affected areas had 2.5 (95% CI: 1.1-5.7) increased odds of being unvaccinated with OPV compared with non-polio AFP case-patients in the same age group in other parts of Syria. Three outbreak response rounds of monovalent OPV type 2 (mOPV2) vaccination were conducted, with governorate-level coverage mostly exceeding 80%. INTERPRETATION: Significant declines in both national and subnational polio vaccination coverage, precipitated by war and a humanitarian crisis, led to a cVDPV2 outbreak in Syria that was successfully contained following three rounds of mOPV2 vaccination. Published by Elsevier Ltd.