Post-Campaign Evaluation of Diphtheria Vaccination Coverage in Somalia Following the 2025–2026 Outbreak Response

Background: Although a protective vaccine is available, diphtheria reemerged in Somalia starting in mid-2023, with an outbreak reported throughout the country in 2025. In response, the Federal Ministry of Health (FMoH) developed a diphtheria outbreak response plan in 2025, launching a vaccination campaign with the first round conducted on 16–20 December 2025 and the second round on 8–13 February 2026. The vaccination campaign was a mass public health push to rapidly deliver Pentavalent and Td vaccines to children in Somalia regardless of past vaccination status, to stop the diphtheria outbreak. During the campaign, under-5 children received Pentavalent vaccines, while 5–15-year-olds received Diphtheria and Tetanus (Td). This study aims to evaluate the post-campaign coverage of diphtheria vaccines in the three most stable states in Somalia, namely the Benadir region, Puntland, and Galmudug states. Methods: The post-campaign coverage survey (PCCS) was conducted from 18 to 21 July 2026 in Benadir, Galmudug, and Puntland states. A two-stage cluster sampling design was employed, whereby 362 clusters were randomly selected from a national sampling frame covering all accessible districts, villages, and nomadic areas across the three states. The sample size was calculated according to the WHO 2018 manual, resulting in the selection of 120 clusters and 1335 households from each state, culminating in a total of 4093 interviews and covering 9184 children. Surveys were carried out by 152 trained personnel equipped with the KoboCollect app for digital data collection. Ethical approval was obtained from the Somali National University Ethical Committee. Results: Among the children, 49.7% were aged 0 to <5 years, and 50.3% were aged 5 to 15 years. Weighted data indicated that 84.1% of children aged 0 to 15 years across the three states received at least one dose of the diphtheria vaccine during the campaign (95% CI: 80.4% to 87.2%). Among those vaccinated, only 25% of children under 5 years of age and 36% of children aged 5 to 15 years received two doses. Vaccination coverage varied significantly by state: Puntland reported the highest coverage at 93.9%, while Galmudug had the lowest at 75.4% (95% CI: 69.2–80.7%), and Benadir showed intermediate coverage at 80.3% (95% CI: 74.5–85.1%). Geographically, internally displaced persons (IDPs) and nomadic populations had the lowest coverage rates, at 71.9% (95% CI: 55.0–84.2%) and 72.6% (95% CI: 57.9–83.7%), respectively. The primary reason for children not being vaccinated was a lack of awareness about the vaccination campaign. Conclusions: Although the diphtheria outbreak response campaign achieved high overall vaccination coverage, important coverage gaps persisted among underserved populations and in Galmudug state. Future outbreak responses should prioritize equitable vaccine delivery, community engagement, and strengthening routine immunization services. Future PCCS surveys should apply locally informed design-effect assumptions to enhance the accuracy and efficiency of coverage estimates.