Temporal trends and Distribution of measles outbreaks in Uganda, 2020-2025

Summary

Background: The World Health Organization (WHO) recommends ≥95% coverage with two doses of measles–rubella (MR) vaccine to interrupt transmission. However, by 2023, WHO/United Nations Children’s Fund (UNICEF) estimates of national immunization coverage (WUENIC) estimates showed Uganda among countries with MR2 coverage (≤50%) below this target, leaving many children susceptible to measles infection. We described temporal and spatial trends in measles outbreaks to identify persistent high-risk areas and programmatic gaps; to inform targeted outbreak control measures.

Methods: We conducted a descriptive analysis of national measles surveillance and immunization data from January 2020 to December 2025. Data sources included outbreak reports from the National Expanded Program on Immunization, and aggregate MR1/MR2 administrative coverage from District Health Information Software 2. Outbreaks were defined as ≥3 IgM-positive cases within 30 days.We summarised case counts using descriptive statistics, calculated annual percentage changes, and assessed temporal trends with Mann–Kendall tests.

Results: From 2020–2025, 3,192 measles cases were reported, 93% (2,970) of whom had received 1 MR dose, while none had received the full two-dose schedule. Cases increased from 48 (1.5%) in 2021 to 1,967 (61.6%) in 2025, though the trend was not statistically significant (τ_b=0.733, p=0.060). Overall, 115/146 (78.8%) districts reported ≥1 outbreak, peaking in 2025 (46 districts, 31.5%). MR1 coverage averaged at 92%, while MR2 improved to 64% by 2025 (τ_b=0.95, p=0.04).

Conclusion: Measles outbreaks persisted during the study period, driven by suboptimal vaccine coverage and resulting immunity gaps among vulnerable populations. Strengthening the second-year-of-life platform and integrating MR2 with co-administered vaccines are essential to close immunity gaps and prevent recurrent outbreaks.

Background

Measles is a highly contagious viral disease transmitted via respiratory droplets, characterized by fever, cough, coryza, conjunctivitis, and a maculopapular rash (1–3). Despite the availability of an effective vaccine for over five decades, measles remains a major global public health concern, particularly in settings with suboptimal immunization coverage (4–6). Achieving ≥95% coverage with two doses of measles–rubella vaccine (MR) is essential for herd immunity and interruption of transmission (7).

Between 2020 and 2025, measles control efforts were undermined by the COVID-19 pandemic, which disrupted routine immunization services worldwide. In 2020 alone, an estimated 22.7 million children missed routine vaccinations; a 19.5% increase from 2019 (8,9), creating what the World Health Organization described as a “perfect storm” for measles outbreaks (10).

Uganda reflects these global challenges. Coverage for first dose of measles-rubella vaccine (MR1) has remained below the 95% elimination threshold, averaging 90% through 2023–2024, while MR2, introduced in 2022, remains suboptimal at approximately 50% coverage by 2024(11). These gaps sustain a large pool of susceptible children, enabling recurrent outbreaks despite localised improvements in MR1 uptake. Additional drivers include cold chain limitations, inequitable access to services in hard-to-reach areas, and delays in outbreak detection (12–15). To inform targeted outbreak control interventions, we analysed temporal and spatial trends in measles outbreaks and assessed immunisation coverage to identify persistent high-risk areas and programmatic gaps.

Methods

We conducted a national descriptive analysis of measles surveillance and immunization data from January 2020 to December 2025 across all 146 districts in Uganda. Data were triangulated from three sources: (1) case-based records of laboratory-confirmed (IgM-positive) measles cases from the Uganda Virus Research Institute (UVRI); (2) Uganda National Expanded Programme on Immunization (UNEPI) surveillance reports to verify outbreak districts and supplement case data; and (3) aggregate MR1 and MR2 administrative coverage from DHIS2.

A measles outbreak was defined per Uganda’s National Technical Guidelines for Integrated Disease Surveillance and Response (3rd Edition) and WHO measles surveillance guidelines as ≥3 laboratory-confirmed (IgM-positive) measles cases within  30 days in the same district or sub-district (16,17).

We summarized cases using descriptive statistics. Annual percentage changes (APCs) were estimated using log-linear regression, and temporal trends assessed using the Mann–Kendall test. Geographic patterns were mapped in QGIS 3.42.1. Coverage of first (MR1) and second dose (MR2) of measles rubella vaccine was compared across outbreak districts to identify high-risk areas.

Permission to analyse the data was obtained from the Uganda Ministry of Health (MoH). In addition, a non-research determination clearance was granted by the U.S. Centers for Disease Control and Prevention (CDC). The investigation was conducted in accordance with applicable U.S. federal regulations governing public health surveillance and data protection (see, for example, 45 C.F.R. part 46; 21 C.F.R. part 56; 42 U.S.C. §241(d); 5 U.S.C. §552a; 44 U.S.C. §3501 et seq.). Further authorization was obtained from the Uganda National Expanded Programme on Immunization (UNEPI) for access to vaccination and surveillance data. As this analysis involved routine program and surveillance data and posed no more than minimal risk to participants, written informed consent was not required. All data were anonymized before analysis, and strict measures were implemented to maintain privacy, confidentiality, and data security throughout the data abstraction and analysis process.

Results

National burden and temporal trends of measles cases, 2020–2025

Between 2020 and 2025, Uganda reported 3,192 measles cases, of which 2,970 (93%) had received 1 MR dose, while none had received the full two-dose schedule Annual cases varied markedly, from 48 (1.5%) in 2021 to 1,967 (61.6%) in 2025. Although an overall upward trend was observed (τ_b=0.73, p=0.060), it was not statistically significant (Figure 1). Year-to-year changes were highly variable, with sharp increases in 2024 (APC=+334%) and 2025 (APC=+152%) following a decline in 2021 (APC=−68%) (Figure 1).

Spatial distribution and trends confirmed measles outbreaks across districts, Uganda, 2020–2025

Overall, 115/146 (78.8%) districts reported ≥1 confirmed outbreak. The number of affected districts fluctuated widely, from 13 (8.9%) in 2020 to a low of 1 (0.7%) in 2021–2022, before rising sharply to 45 (30.8%) in 2024 and 46 (31.5%) in 2025 (τ_b=0.55, p=0.181). Twenty-two districts experienced recurrent outbreaks, including Buvuma, Isingiro, Jinja, Kamwenge, Kiryandongo, Mbale, Manafwa, Kikuube, Butaleja, Kakumiro, Mpigi, Moroto, Napak, Nakaseke, Kanungu, Namutumba, Lamwo, Kampala, Koboko, Madi-Okollo, Yumbe, and Sembabule during the study period (Figure 2).

Spatial overlay of Measles-Rubella vaccination coverage by outbreak districts, Uganda, 2020–2025

Over the six-year period, MR1 coverage averaged at 92%, while MR2 coverage, introduced in 2022, statistically increased from low baseline (22%) to 64% by 2025 (τ_b=0.95, p=0.04). Spatial overlay analysis showed that outbreaks occurred across all coverage categories, including districts with MR1 coverage ≥95% (Figure 3).

Discussion

Our analysis demonstrates persistent measles transmission in Uganda from 2020 to 2025, marked by a 40-fold increase in cases, spread to 78.8% of districts, and ongoing immunity gaps driven by suboptimal vaccination coverage. The rise from a single outbreak-affected district in 2021 to 46 districts in 2025 suggests sustained local transmission rather than isolated importations. This pattern aligns with global post-COVID-19 trends, where disruptions in routine immunization created susceptible cohorts, resulting in explosive outbreaks upon measles reintroduction (8,9,18).

That 93% of cases had received at least one MR dose may seem paradoxical but reflects the limitations of a single-dose schedule. With 5–10% primary vaccine failure and ~5% secondary failure due to waning immunity (19–22) , 10–15% of children remain susceptible even in a population with 92% MR1 coverage. This highlights the critical role of routine MR2 in addressing primary vaccine failures and boosting immunity, a strategy proven effective in global measles elimination efforts (23).

Outbreaks in districts reporting ≥95% MR1 coverage can be explained by two factors: (1) administrative coverage often overestimates true immunity due to inaccurate denominators, inflating coverage by 10–20% (24); and (2) 5–10% of vaccinated children fail to develop protective immunity (19,20). Although MR2 coverage improved to 64% by 2025, systemic challenges remain.

Study limitations: Administrative coverage data from DHIS2 may not reflect true immunity due to inaccurate denominators, unregistered children, or incomplete reporting. We focused on temporal trends and relative changes rather than absolute coverage, reducing sensitivity to systematic errors.

Conclusion

Measles persisted in Uganda from 2020 to 2025 due to suboptimal vaccine coverage, leaving many children vulnerable. Strengthening the second-year-of-life platform by integrating MR2 with routine child health services, along with targeted follow-up, could close immunity gaps, achieve ≥95% MR coverage, and advance measles elimination efforts in Uganda.

Conflicts of interest: The authors declared no conflicts of interest.

Acknowledgements: We acknowledge the Uganda National Expanded Programme on Immunization, Uganda Virus Research Institute, and Ministry of Health Division of Health Information for data access and technical support. We thank district health teams for their commitment to measles surveillance and outbreak response.

Author contributions: SN conceptualized the study and led data collection, analysis, and writing. RM, and BK, provided technical supervision and Bulletin review. GB, DK, NM, MDN, YN, and FN supported data analysis, and report writing. All authors approved the final version.

Copyright: Materials in the Uganda Public Health Bulletin are public domain and may be reproduced with appropriate citation.

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