Chikungunya vaccine approval in Brazil: navigating through epidemiological challenges and immunisation strategies

Chikungunya virus (CHIKV) can cause acute arboviral illness, usually accompanied by severe polyarthralgia. In 2025, live-attenuated CHIKV vaccine Ixchiq® (Valneva, Saint-Herblain, France) was authorised for use in Brazil, where CHIKV often co-circulates with other arboviruses. A central public health question emerges: how should this vaccine be optimally deployed in a country characterised by hyperendemic transmission, frequent underdiagnosis, and marked regional disparities? We conducted an epidemiological analysis using notified CHIKV cases from the Notifiable Diseases Information System (SINAN) and socioeconomic indicators from the Brazilian Human Development Atlas. This framework enabled the identification of municipal clusters with shared epidemiological and socioeconomic profiles, allowing exploration of the relationship between disease notification rate and social health determinants. Our results showed that CHIKV transmission exhibited a cyclic pattern with geographic expansion toward the Southeast/South - Brazil's most densely populated regions characterised by low population immunity. Cluster analyses showed that the greatest disease burden is concentrated in socioeconomically disadvantaged municipalities, particularly in the Northeast, where healthcare disparities may further impact diagnostic capacity. Based on the obtained results, we believe in a hybrid immunisation strategy starting from high-incidence municipalities in the northeast and reaching major urban centres in the southeast in order to prevent larger outbreaks. Implementation must account also for current vaccine contraindications in high-risk groups and be guided by real-time epidemiological and entomological surveillance.