Estimating age-stratified measles susceptibility using the screening method: an example from 2018-21 measles resurgence in Brazil.

OBJECTIVES: Characterizing susceptibility profiles across age groups and administrative units is essential for targeted vaccination and control of resurgent vaccine-preventable diseases like measles, but is often limited by the lack of historical vaccination records. METHODS: We proposed a methodology based on the screening method that uses routine surveillance data, such as case age and vaccination status, along with an estimate of vaccine effectiveness, to estimate age-stratified susceptibility to a vaccine-preventable disease. RESULTS: Applying this method to the 10 most affected Brazilian municipalities by measles resurgence in 2018-21, we signal municipalities that have a population immunity below the herd immunity threshold, along with the age groups with the largest susceptible cohorts. Some municipalities show an overall large susceptibility, while others concentrate susceptible individuals in the age cohorts >20 years, as a result of past low vaccine coverage. CONCLUSION: The proposed methodology is a low-cost tool to estimate susceptibility using readily available surveillance data, allowing for identification of susceptible age cohorts, even in the absence of historical vaccination data. The results obtained offer actionable insights for designing vaccination strategies in Brazil as well as similar epidemiological contexts, as the methodology can be easily applied on similar datasets.