Dengue Vaccine Effectiveness: Results from a Six-Year Population-Based Cohort Study in Southern Brazil

The alarming growth of dengue worldwide and its social and economic impact have demanded more effective responses for its prevention and control. Currently, the first vaccine approved in Brazil for its prevention, Dengvaxia®, was administered to a target population of around 500,000 residents in southern Brazil. This study reports its effectiveness after a six-year follow-up period from August 2016 to July 2022. Dengue vaccination campaign was carried out in a target population of individuals aged 15–27 in 28 municipalities and 9–44 years in the other two. In this population-based cohort study, exposure to the vaccine included groups with different numbers of doses and adherence to the complete schedule. The primary outcome was probable dengue case. Other endpoints included laboratory- confirmed dengue, serotype, dengue with warning signs or severe illness, and hospitalization. Approximately 60.4% of the participants received at least one vaccine dose. A total of 50,658 probable dengue cases (PDC) were notified of which 15,131 were laboratory-confirmed dengue cases. Overall effectiveness for at least one dose was 33.7% (95% CI: 32.5–34.9) for PDC and 20.1% (95% confidence interval [CI]: 17.1–22.9) for laboratory-confirmed cases. Greater vaccine effectiveness was observed in older individuals and for the DENV-4 and DENV-1 serotypes. The vaccine showed no effectiveness against DENV-2; no DENV-3 cases occurred. A lower hospitalization rate was observed among the vaccinated group. Differences in the incidence of severe dengue cases and warning signs could not draw a definite conclusion. Vaccination was associated with a one-third reduction in the incidence of probable dengue cases. By serotypes, the reduction was significant only for DENV-1 and DENV-4. Author Summaries Outcomes resulting from dengue mass vaccination remains limited. Study on Dengvaxia®’s effectiveness in a target population of 501,000 with unknown serostatus. Dengue risk reduction was significant for DENV-1 and DENV-4.