Rubella burden hidden within measles case-based Surveillance in Rivers State, Nigeria: A Retrospective Comparative Analysis

Background: Rubella remains an under-recognized vaccine-preventable disease in many low- and middle-income countries, including Nigeria, where routine rubella vaccination coverage remains suboptimal. In many African countries, rubella surveillance is conducted through integrated measles case-based surveillance systems, leading to undetected rubella transmission among suspected measles cases. This study assessed the burden and epidemiological characteristics of rubella identified within measles surveillance data in Rivers State, Nigeria.
Methods: A retrospective comparative analysis of measles case-based surveillance data from Rivers State, Nigeria, was conducted using laboratory surveillance records from January 2020 to December 2024. Data were extracted from the integrated measles-rubella surveillance database and analyzed using Statistical Package for Social Sciences (SPSS) version 25. Laboratory-confirmed measles and rubella cases were identified using measles immunoglobulin M (IgM) and rubella IgM serology results. Descriptive statistics were used to summarize demographic and temporal characteristics. Comparative analyses were performed using the Chi-square and Mann–Whitney U tests, and logistic regression was used to identify factors associated with rubella positivity among measles-negative suspected cases. Statistical significance was set at p<0.05.
Results: A total of 1,520 suspected febrile rash illness cases were analyzed during the study period. Of these, 297 (19.5%) were laboratory-confirmed measles cases, while 102 (6.7%) were laboratory-confirmed rubella cases. Among the 1,172 measles-negative cases, 102 (8.7%) were positive for rubella IgM, demonstrating a hidden but measurable burden of rubella within the measles surveillance system.
The median age of measles-confirmed cases was 10.5 years (IQR: 4–25 years), compared with 7 years (IQR: 4–18 years) among rubella-confirmed cases (p=0.031). Males constituted 54.9% of measles-confirmed cases and 49.0% of rubella-confirmed cases. Measles positivity peaked in 2022, while rubella transmission persisted throughout the study period.
In the multivariable logistic regression analysis, age less than 15 years was independently associated with rubella positivity among measles-negative suspected cases (AOR: 1.69; 95% CI: 1.02–2.81; p=0.041).
Conclusion: A hidden but measurable burden of rubella exists within measles case-based surveillance in Rivers State, Nigeria. Persistent rubella transmission among measles-negative febrile rash illness cases underscores the importance of integrated measles-rubella surveillance systems and strengthened laboratory confirmation. The findings support enhanced rubella surveillance, improved routine immunization strategies, and accelerated scale-up of rubella-containing vaccines in Nigeria.