An outbreak of circulating vaccine derived poliovirus in Yemen, 2011-2012

Abstract

Background: Yemen has been polio free since 2006. However, recently civil unrest and popular uprisings across the country arose with intermittent armed conflicts in the Northern governorates especially Sa’ada led to low routine immunization coverage and suspending supplementary immunization activities (SIAs). Such widening immunity gap known to be predisposing factors for Circulating Vaccine Derived Poliovirus (cVDPV) outbreak. We reviewed acute flaccid paralysis (AFP) cases to identify any emerging cVDPV Methods & Materials: Cases of AFP identified through routine AFP surveillance from April 8,2011,through 24 August 2012 were investigated for any fecal excretion of cVDPV. WHO-recommended virological classification scheme was used. Results: Nine cases of laboratory confirmed type 2 cVDPV and 2 cases type3 cVDPV were identified from six governorates: Sa’ada (1.3/100,000 <15 years children), Amran (0.2/100,000), Hajjah (0.1/100,000), Ibb (0.08/100,000), Sana’a city (0.07/100,000) and Hodeida (0.07/100,000). The corresponding third dose of Oral polio vaccine (OPV) coverage is 49%,78%,89%,87%,83% and 80% respectively. The median age was 22 months with a male to female ratio of 2.7:1. Most reported symptoms were fever (100%), asymmetrical paralysis (73%), and intact sensation (73%). OPV immunization status among cases was: zero dose: 36%, < 3 doses: 36%, and ≥ 3 doses: 27%. Conclusion: The rate of cVDPV is highest in the armed conflict Sa’ada and its neighboring Amran where the lowest vaccination coverage was also achieved. There is an urgent need to maintain high OPV coverage in at-risk populations to prevent the spread of endogenous cVDPV. Sensitive and timely AFP surveillance systems are essential to ensure quick identification of cVDPV and response