Real-World Effectiveness of Dengue Vaccine During Brazil's 2024 Outbreak

An international research team has demonstrated that the tetravalent dengue vaccine, known as Qdenga, proved to be significantly effective in protecting against dengue during the large 2024 epidemic in São Paulo, Brazil. The study, published in The Lancet Infectious Diseases, offers critical insights into the vaccine's performance outside of clinical trials, under actual epidemiological conditions.

Led by Dr. Otavio Ranzani from the DataHealth Lab at the Sant Pau Research Institute and Dr. Julio Croda from FioCruz, the research analyzed data from over 90,000 adolescents who presented with acute fever symptoms and underwent specific laboratory testing for dengue. Using a test-negative case-control design, the study compared vaccination rates between those who tested positive and negative for dengue. The findings revealed that after a single dose, the vaccine provided approximately 50% protection against symptomatic dengue, which increased to 62% after the second dose. Additionally, it reduced hospitalizations due to dengue by 68%. Notably, protection began 14 days after the first dose and was sustained for the initial three months, emphasizing the importance of completing the full two-dose schedule for enduring immunity.

The study took place during a major outbreak that caused tens of thousands of cases in São Paulo, with vaccination campaigns prioritizing adolescents aged 10 to 14, given their high risk and role in disease transmission. The vaccination effort involved nearly 690,000 doses, and the findings underscore the vaccine's capacity to mitigate the health burden during epidemics.

While the study's strengths include the large sample size and the real-world epidemic context, some limitations were acknowledged. Vaccine coverage was relatively low, limiting detailed analysis of effectiveness after the second dose, and data on prior dengue immunity among adolescents was unavailable. Furthermore, the circulating serotypes during the outbreak primarily included DENV-1 and DENV-2, preventing assessment against all four dengue virus serotypes.

Beyond Brazil, the study's implications are globally relevant. It is the first to provide real-world evidence of Qdenga’s effectiveness, expanding the understanding from previous controlled trials. As climate change facilitates the spread of the Aedes mosquito, and outbreaks occur increasingly in non-endemic regions like Europe, this vaccine could be vital in protecting travelers and preventing localized transmissions. European countries such as France and Italy have reported imported dengue cases and some local transmission events, highlighting the importance of effective vaccination strategies.

The findings support the use of Qdenga in emergency and routine immunization campaigns to control outbreaks, especially in endemic regions. The observed protection from just one dose within weeks can help reduce disease spread and healthcare system strain. Moreover, the vaccine's potential role in traveler prophylaxis and in preventing autochthonous outbreaks extends beyond endemic countries, offering a proactive tool in global dengue prevention.

Dr. Ranzani emphasizes that despite certain limitations, the consistent evidence of vaccine efficacy against both mild and severe dengue underscores its value in public health. Ensuring full vaccination with the recommended two-dose schedule is critical for long-term protection, and these insights can guide policymakers and health authorities in vaccination planning and response efforts.

For more details, refer to the study: Otavio T Ranzani et al, Effectiveness of the TAK-003 dengue vaccine in adolescents during the 2024 outbreak in São Paulo, Brazil: a test-negative, case–control study, The Lancet Infectious Diseases (2025).