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. ### Competing Interest Statement The research received funding from SANOFI Pasteur, where the vaccine was developed and produced. The authors received grants to support the development of the research and declare a conflict of interest. However, this financial support did not influence the ethical commitments of the researchers, in the analysis and presentation of results, being faithful to what was found. Furthermore, the research was based on secondary data from government institutions and the researchers confirm that they will adhere to PLOS policies on sharing data and materials. ### Funding Statement Yes ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This study was approved by the Research Ethics Committee of the Federal University of Parana (Number 2,308,662). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes The databases used in the research will be made available in a repository at the Universidade Federal do Paraná, as soon as the publication of the article is confirmed.