Assessment of vaccine effectiveness during measles outbreak in the Federation of Bosnia and Herzegovina, 2014-2015

Objective: Between February 2014 and September 2015 a large measles outbreak (5,084 cases) occurred in the Federation of Bosnia and Herzegovina (FB&H). The aim of this study is to assess the effectiveness of routine measles vaccination in the FB&H. Methods: We conducted an analysis of the resurgence period surveillance data and a retrospective cohort study involving primary school aged children in randomly selected schools. Results: Measles cases occurred among all age groups, mostly among the unvaccinated. Among fully immunized, 2.1% contracted measles. Measles vaccine effectiveness was high. The study indicates that one dose reduced the risk for measles by 91.9% (95% CI: 81.4-96.4%), two doses reduced the risk by 97.3% (95% CI: 95.5-98.4%). No evidence of waning immunity was found. Our survey reveals that a significant number of children had no immunization status registered. Conclusions: The results of this study suggest that the resurgence was likely caused by an accumulation of measles-susceptible children not being vaccinated. This vaccine effectiveness study does not support possible vaccination failure as a contributing factor.