Comparative epidemiological analysis of the 2023 and 2025 Marburg virus disease outbreaks in Kagera Region, Tanzania

<h2>Abstract</h2><h3>Background</h3> Marburg Virus Disease (MVD) is a severe zoonotic hemorrhagic fever with high case fatality rates (CFR). Tanzania's Kagera region experienced MVD outbreaks in 2023 and 2025, offering critical insights into evolving epidemiological trends and the effectiveness of response strategies. This study compares these outbreaks to inform future preparedness. <h3>Methods</h3> We conducted a retrospective analysis of official situation reports from the Tanzanian Ministry of Health, WHO, and other health authorities. Data on sociodemographic, CFR, transmission dynamics, response metrics (alerts, samples, contacts), and response timelines were analyzed using descriptive statistics, chi-square, and t-tests. The time-varying reproduction number (Re) was estimated using the EpiEstim R package <h3>Results</h3> The 2025 outbreak had a significantly higher CFR (100%) compared to 2023 (66.7%) (p<0.05). Demographic shifts included a decrease in median age from 35 to 30 years and a reversal in sex distribution, with females more affected in 2025 (70%) versus males in 2023 (66.7%) (p=0.03). The outbreak epicenter shifted from Bukoba to Biharamulo district. While the scale of response increased dramatically in 2025 (alerts: 131 to 1,218; samples tested: 78 to 202), the initial response was delayed, with a longer interval from symptom onset to outbreak declaration (37 days in 2025 vs. 10 days in 2023) and initial diagnostic confusion. Mean Re was <1 throughout the 2023 outbreak but exceeded 1 mid-epidemic in 2025. <h3>Conclusion</h3> The 2025 outbreak was characterized by increased lethality and distinct demographic shifts. The response demonstrated a significant scale-up in surveillance and international coordination. However, critical challenges in early detection, diagnostic confirmation, and the efficiency of converting alerts into traced contacts highlight the need for a balanced strategy that couples technological innovation with fundamental strengthening of health system core functions.