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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. 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. 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%. 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. [ABSTRACT FROM AUTHOR]

A community-based serosurvey was conducted among children ages 6-59 to assess population immunity in Jordan's high-risk areas following the Middle East polio outbreak response. The survey was a two-stage cluster-quota sample with high risk areas as the primary sampling units. High-risk areas included border and hard-to-reach areas, and areas with a high proportion of refugees, mobile communities and/or low coverage during previous immunization campaigns. Population immunity to poliovirus was high overall. In high-risk areas, Type 1 seroprevalence = 98% (95% CI = 96, 99), Type 2 = 98% (95% CI = 96, 99) and Type 3 = 96% (95% CI = 94, 98). Seroprevalence was higher in the refugee camps: Type 1 seroprevalence = 99.6% (95% CI = 97.9, 100); Type 2: 99.6% (95% CI = 97.9, 99.9), and Type 3: 100% (95% CI = 100,100). The vigilance that the Jordan Ministry of Health has placed on locating and vaccinating high-risk populations has been successful in maintaining high population immunity and averting polio outbreaks despite the influx of refugees from Syria.