Real-World Effectiveness of the Dengue Vaccine Qdenga During Brazil’s 2024 Outbreak
A Brazilian study published in The Lancet Infectious Diseases provides the first real-world evidence of Qdenga’s effectiveness after its approval. Conducted during the 2024 dengue surge in São Paulo, the research tracked outcomes among tens of thousands of adolescents and sheds light on how the vaccine performs outside controlled trials.
Study design and setting
Led by Otavio Ranzani from DataHealth Lab and Júlio Croda from Fiocruz, the team analyzed vaccination and infection data in the state of São Paulo, the epicenter of the outbreak that year. Health authorities prioritized vaccination for 10- to 14-year-olds, a group that accounted for a large share of symptomatic cases and hospitalizations in endemic areas. Across the campaign, about 690,000 doses of Qdenga were administered as part of a two-dose schedule.
Methods
The researchers examined more than 90,000 adolescents who presented with fever and underwent laboratory testing for dengue. By comparing vaccination status among those who tested positive versus negative for dengue, they estimated the vaccine’s effectiveness in real-world conditions—informing how well Qdenga works when used as part of a routine immunization program.
Key findings
Results show that after just one dose, Qdenga reduced symptomatic dengue by about 50 percent. A second dose increased this protection to roughly 62 percent. Most notably, hospitalizations were reduced by 68 percent after the first dose. Researchers noted that protection began 14 days after the initial vaccination, remained through the first three months, and then waned. This pattern underscores the importance of completing the recommended two-dose schedule to maintain longer-lasting protection.
Vaccine details and broader context
Qdenga is a tetravalent dengue vaccine, meaning it targets up to four dengue virus serotypes. This broad coverage is particularly important in Brazil, where multiple strains circulate and shift during outbreaks. The Lancet Infectious Diseases study adds to the global understanding of how well this vaccination strategy translates into population-level impact in real-world settings.
Context and implications
Until now, evidence for Qdenga’s effectiveness came mainly from phase 3 clinical trials. This study provides early real-world data confirming the vaccine’s potential to reduce severe outcomes during an outbreak. The 2024 dengue wave in Brazil saw about 6.6 million cases and at least 6,239 fatalities, highlighting the urgent need for effective tools. The findings support continued use of Qdenga in adolescent vaccination campaigns and reinforce the value of completing the two-dose regimen to maximize protection.
Public health takeaways
For health authorities, the study offers actionable insights: vaccinate adolescents promptly, emphasize completing the two-dose series, and maintain high vaccination coverage in high-burden areas to curb hospitalizations and severe disease during future outbreaks. Ongoing surveillance will be essential to monitor longer-term protection and to adapt strategies as the virus evolves.
Conclusion
The Brazilian experience with Qdenga during the 2024 dengue outbreak provides a critical milestone: real-world effectiveness of a tetravalent vaccine can translate into meaningful reductions in hospitalizations, even amid a surge. As vaccination campaigns continue, the two-dose schedule remains central to safeguarding adolescents and reducing the burden of dengue in Brazil and other endemic regions.
