Introduction: Circulating Vaccine Derived Poliovirus (cVDPV), is a genetic mutation of the Sabin virus. Sierra Leone reported its last case of wild polio virus in 2010. However, in December 2020, the national disease surveillance program was notified of three people with acute flaccid paralysis who had cVDPV2. We investigated to identify the source, determine the magnitude of the outbreak and risk factors.
Methods:We assessed the clinical and vaccination status of the cases, searched for trivalent-OPV (tOPV) and monovalent-OPV (mOPV2) in the health facilities serving the affected communities. We searched for additional cases in the affected communities and collected stool specimens from contacts of case-patients. We assessed the cold chain management and routine immunization services. We conducted a vaccination coverage survey using the WHO zero-dose case investigation form in 128 randomly selected households of the affected communities.Results: Case-patients were 26-month-old male from Kambia, 39-months-old female from Western Area rural, and 15-month-old female from Tonkolili district. All had fever and acute paralysis. No tOPV or mOPV were found in the facilities. Infections in two case-patients were genetically linked to cases in Guinea and Cote d'Ivoire. There was no history of travel within 21-days of onset of symptoms for all cases. All received three doses of OPV, two received one dose of Inactivated Polio Vaccine (IPV). Fourteen (47.4%) contacts tested positive for poliovirus type 2. Cold chain status at facilities was poor. Only 47% (44/93) of children 0-59 months received three doses of OPV and 48% (30/63) received one dose of IPV.
Conclusion:The cVDPV2 may have been imported from neighbouring countries. OPV and IPV coverage was low, and poor cold chain may have reduced the vaccine potency. We conducted enhanced surveillance and prepared for nOPV2 vaccination. We recommend strengthening AFP surveillance, routine immunization and improve cold chain management.