Evaluation of Uganda’s 120-day response to cVDPV2 polio outbreak in Mbale Region, June–September 2024

Introduction: In May 2024, Uganda confirmed circulating vaccine-derived poliovirus type 2 (cVDPV2) from an environmental sample in Mbale City, Eastern Uganda. Such detection signals possible silent transmission and requires rapid response under World Health Organization (WHO) outbreak Standard Operating Procedures, which aim to interrupt transmission within 120 days. We evaluated Uganda’s response in Mbale sub-region against these WHO response standards. Methods: We conducted a descriptive evaluation of the response using WHO polio outbreak standards as the benchmark. We assessed timeliness of notification and outbreak declaration, epidemiologic and risk assessments, surveillance performance, and immunization response activities. Acute Flaccid Paralysis (AFP) surveillance and routine immunization indicators were compared between the 120-day pre-response and response periods using DHIS2 data from 17 districts in Mbale sub-region. Results: Uganda notified WHO within 24 hours of laboratory confirmation, meeting the WHO notification benchmark. Formal outbreak declaration occurred five days after confirmation, exceeding the 72-hour benchmark by two days. Epidemiologic investigation and risk assessment were initiated within 24 hours. During the 120-day response period, 227 AFP cases were detected compared with 36 during the preceding 120-day period, while the NPAFP rate increased from 1.4 to 8.8 per 100,000 children aged <15 years. The proportion of districts achieving ≥95% DPT1 coverage increased from 76% to 82%, while the proportion achieving ≥95% DPT3 coverage increased from 52% to 82%. Two rounds of nOPV2 supplementary immunization activities were implemented within the response period, with reported administrative coverage of 118% and 114%, respectively; independent monitoring estimated coverage at 92.4% inside and 89.4% outside households in round one and 99.4% and 98.0%, respectively, in round two. Conclusion: Uganda’s response largely met key WHO outbreak response standards, including timely notification, rapid investigation, enhanced AFP surveillance, and implementation of high-coverage nOPV2 vaccination campaigns. Surveillance and selected routine immunization indicators improved during the response period.