Measles Vaccination Coverage and Protective Effectiveness in the Amhara Regional State, Ethiopia, 2019-2024

Abstract Background: Despite the availability of an effective vaccine, measles remains a major public health problem in Ethiopia, with recurrent outbreaks reported in several areas in Amhara Regional State. Understanding measles vaccination coverage and real-world protective effectiveness is critical for assessing immunization program performance and guiding elimination strategies. Therefore, this study was conducted to determine the regional measles vaccine coverage and the vaccine protective effectiveness level in the region. Methods: A retrospective test-negative case-control analysis of measles surveillance data and retrospective analysis of district health information system 2 (DHIS2) data from 2019-2024 was employed to determine vaccine effectiveness and vaccine coverage respectively. Measles vaccine coverage was determined by dividing the number of children vaccinated as numerator to the expected number of children legible for vaccination as denominator. Measles vaccine effectiveness level was determined using field evaluation approaches of vaccine effectiveness. The adjusted vaccine effectiveness was calculated using the multivariable logistic regression after adjustment of potential confounders, including age, sex, residence, and outbreak year. Results: Measles vaccination coverage for both vaccine doses showed variation across geographic locations, time periods with clear seasonal and monthly differences. A total of 3417 participants comprising 2528 cases and 889 controls were enrolled in the analysis of measles vaccine effectiveness. A cumulative vaccine effectiveness estimates was 67% in the region with a clear variation across different years. The subgroup analysis showed comparable level of measles vaccine effectiveness (66.6% vs 66.9%) between males and females. The higher level of measles vaccine effectiveness estimates, 76.2%, among children aged 9 months-2 years while lower vaccine effectiveness estimates, 41.1%, was demonstrated among individuals aged ≥15 years. Conclusion: It was identified a high and increasing administrative measles vaccine coverage with geographical disparities. The estimated overall vaccine effectiveness level was low far apart from the expected level of protection against the vaccine coverage. Two vaccine doses administered individuals had a higher protection level than a single dose received individuals. There was a better vaccine protection level during the recent periods of vaccination compared to earlier periods. Therefore, it is important to increase the access of vaccines to the most unreachable areas maintaining vaccine integrity during delivery. Vaccine coverage should be monitored based on the head count of legible children in each district in the region. It is also important to strengthen the routine measles vaccination practices in any situations and booster dose should also be administered for those older age children.