Background: Measles vaccination is the most important public health intervention and a cost-effective strategy to reduce morbidity and mortality in under-five children. Although Ethiopia's government developed a measles elimination strategic plan by 2020, the full coverage of immunization was 43 %. Therefore, this study aimed to identify determinants of second-dose measles vaccination (MCV2) dropout among children aged 24-35 months in East Bale Zone, Ethiopia.

Method: A community-based matched case-control study was conducted among 351 children (117 cases and 234 controls). Children who received the first dose of measles vaccine but did not receive the second dose were cases, and children who received both doses of measles vaccine were control. The matches were based on age and residence. The data were collected using a structured questionnaire, entered into Epi Data 3.1, cleaned, exported, and analyzed using Stata version 16.1. A multivariable conditional logistic regression analysis was performed. Variables with a P value of <0.05 were considered significant determinants of the dependent variable at the 95 % confidence level.

Results: Mothers who were unable to read and write (mAOR: 4.0; 95 % CI: 1.59-10.2), did not receive counseling (mAOR: 3.19; 95 % CI: 1.62-6.27), spent ≥30 min to reach health facilities (mAOR; 2.76, 95 % CI: 1.25-6.1), and did not attend postnatal care (mAOR; 3.46, 95 % CI: 1.58-7.57) were significantly and positively associated with second-dose measles vaccination dropout. In addition, mothers who had poor knowledge of second-dose measles vaccination (mAOR; 3.20, 95 % CI: 1.50-6.70) and waited more than an hour for measles vaccination at health facilities (mAOR; 2.61, 95 % CI: 1.0-6.20) were significantly more likely to experience second-dose measles vaccine dropout.

Conclusions: The key factors associated with second-dose measles vaccination dropout are maternal illiteracy, lack of PNC, inadequate maternal knowledge and poor counseling about MCV2 vaccination, long distances travel to healthcare facilities and extended waiting times at vaccination providing sites. Health extension workers emphasize strengthening home visit programs in catchment households to improve mothers' awareness of measles vaccination.