Dengue Vaccine Effectiveness: Results from a 6-Year Population-Based Cohort Study in Southern Brazil

The alarming growth of dengue worldwide, as well as its social and economic impact, has necessitated effective responses for its control. Brazil, the second country to use Dengvaxia® (Sanofi Pasteur, Paris, France) after the Philippines, has offered the vaccine to ∼500,000 residents in 30 municipalities, with ∼300,000 being vaccinated. In this population-based cohort study, the vaccine's effectiveness (VE) is reported after a 6-year follow-up for a vaccination campaign. The primary outcome was probable dengue case (PDC). Laboratory-confirmed dengue, serotype, warning signs, and hospitalization were considered secondary endpoints. Approximately 60% of participants received at least one vaccine dose. A total of 50,658 PDCs were identified, of which 15,131 were laboratory-confirmed dengue cases. Overall, the VE was 34% (95% CI: 33% to 35%) for PDCs and 20% (95% CI: 17% to 23%) for laboratory-confirmed cases. Greater VE was observed in older individuals. Vaccination was effective in reducing dengue virus (DENV)-1 and DENV-4 cases but not DENV-2 cases. No DENV-3 cases were registered. Among the 1,129 hospitalizations, 619 (54.8%) occurred within the vaccinated population, including 16 severe cases, whereas 510 (45.2%) hospitalizations occurred within the non-vaccinated population, with 18 severe cases. The VE for PDC hospitalizations was 16.5% (95% CI: 5.5% to 26.3%). Five and nine dengue-related deaths occurred within the vaccinated and non-vaccinated populations, respectively. The low incidence of severe cases and warning signs compromised accuracy. Vaccination with at least one dose was associated with approximately a one-third reduction in PDC incidence and a significant reduction in DENV-1 and DENV-4 cases. Despite the VE falling below 50%, vaccination may be justifiable in regions with high disease burden.