Overview
During Brazil’s intense dengue surge in 2024, a tetravalent vaccine known as Qdenga was used in a real-world setting to protect adolescents. Researchers reported that vaccination reduced hospitalizations by up to 68% among those who contracted dengue, marking the first real-world evidence of Qdenga’s effectiveness after its authorization. The campaign unfolded against a backdrop of tens of thousands of cases and a substantial dengue burden across the country.
Vaccination campaign and target group
Health authorities prioritized adolescents aged 10 to 14, a group that accounts for a significant share of symptomatic dengue and hospitalization risk in endemic areas. Over the year, the campaign administered roughly 690,000 doses of the tetravalent vaccine, which contains four attenuated variants of the dengue virus. The aim was to curb severe disease during the surge while individuals completed the recommended immunization schedule.
Study design and setting
The investigation was led by Otavio Ranzani of the DataHealth Lab at the Instituto de Investigação Sant Pau and Júlio Croda from Fiocruz. Conducted in São Paulo, the epicenter of the 2024 outbreak, the study examined more than 90,000 adolescents presenting with acute fever and who underwent laboratory testing for dengue. By comparing the vaccination status of those who tested positive with those who tested negative, researchers estimated real-world vaccine effectiveness in everyday clinical conditions.
Key findings
Effectiveness against symptomatic dengue after the first dose was about 50%, rising to 62% after the second dose. Most notably, vaccination reduced hospitalizations by 68% after the first dose. The protective effect began 14 days after the initial dose and persisted through the first three months, waning thereafter. These results reinforce the importance of completing the two-dose regimen for longer-lasting protection.
Implications for public health
The study provides the first real-world evidence of Qdenga’s effectiveness post-authorization, complementing phase 3 trial data. In Brazil, prior to vaccination, the country recorded a record 6.6 million dengue cases and more than 6,000 deaths in the previous year, underscoring the potential impact of vaccination campaigns during outbreaks.
Policy and practice implications
Health authorities’ prioritization of adolescents and the administration of tens of thousands of doses demonstrate the feasibility of rapid, targeted vaccination during a surge. The results highlight the value of maintaining adherence to the two-dose schedule to achieve more durable protection and inform dengue-endemic countries’ immunization strategies moving forward.
Limitations and future research
As an observational real-world study, residual confounding cannot be fully excluded. Ongoing surveillance is needed to assess long-term effectiveness, potential waning beyond three months, and performance in diverse populations and settings. Further data will help refine recommendations on booster timing and deployment during future outbreaks.
Conclusion
Published in The Lancet Infectious Diseases, the study provides robust real-world evidence that the Qdenga dengue vaccine can substantially reduce hospitalization risk during outbreaks. This reinforces vaccination as a critical tool in Brazil’s ongoing fight against dengue and offers valuable lessons for dengue control strategies worldwide.
