Characterising the 2023 chikungunya outbreak in Paraguay and the potential impact of a vaccine campaign

There now exists a licensed chikungunya vaccine, however, it remains unclear if it could be deployed during outbreaks to reduce the health burden. We used an epidemic in Paraguay as a case study. We conducted a seroprevalence study and used models to reconstruct epidemic transmission dynamics, providing a framework to assess the theoretical impact of a vaccine had it been available. We estimated 33.0% (95% CI: 30.1-36.0) of the population became infected during the outbreak, 6.3% (95%CI: 5.8-6.9) of which were detected by the surveillance system, with a mean infection fatality ratio of 0.013 % (95%CI: 0.012-0.014). A disease-blocking vaccine with 75% efficacy deployed in 40% of > 12-year-olds over a three-month period would have prevented 34,200 (95% CI: 30,900-38,000) cases, representing 23% of cases, and 73 (95%CI: 66-81) deaths. If the vaccine also leads to infection blocking, 88% of cases would have been averted. These findings suggest the vaccine is an important new tool to control outbreaks.