Abstract
<title>Abstract</title> <p>Brazil bears one of the largest chikungunya burdens in the Americas, and the 2024–25 wave expanded further south than any prior outbreak, yet evidence to guide vaccine rollout targeting is lacking. We analyzed 1,235,424 confirmed cases reported to SINAN (2015–2025) across 5,570 municipalities using a Bayesian hierarchical spatiotemporal model and age- and sex-stratified Cox models. Transmission epicenters shifted from the Northeast (2016–17) to the Central-West (2024–25) with persistent spatial clustering. Cases concentrated among adults aged 25–55, whereas post-hospitalization mortality rose steeply with age (hazard ratio 10·57, 95% CI 7·64–14·62 for ages ≥80 versus 20–29). Transmission intensity and case fatality were geographically decoupled. Because the populations contributing most reported cases are not those at highest risk of death, we derived a municipality-level allocation framework defining transmission-control, clinical-preparedness, and combined-priority zones, which is an actionable, updatable basis for targeting the ongoing pilot rollout.</p>