Fighting dengue fever amid the epidemic in Brazil: a vaccine reduces infections and hospitalizations

BarcelonaLast year, there was a major dengue epidemic in several South American countries, with tens of thousands of cases reported in large cities like São Paulo and Buenos Aires. In this context of rising cases, an international team of researchers led by the Sant Pau Research Institute tested the Qdenga vaccine against the disease. Until then, it had shown promising results in controlled clinical trials but had never been evaluated under the pressure of an explosion of infections like that of the 2nd. The vaccine has passed the test with flying colors: it managed to significantly reduce symptomatic cases and hospitalizations at the epicenter of the epidemic.

"The message is clear: the vaccine works and can protect against mild and severe dengue," says Otavio Ranzani, head of the DataHealth Lab group at the Sant Pau Research Institute and leader of the study published this Wednesday. The Lancet Infectious Diseases. Specifically, the research results show that symptomatic cases were reduced by half among those who received one dose and by 62% among those who received two. Furthermore, hospitalizations fell by 68% among immunized individuals: a very important factor to keep in mind, since dengue outbreaks can quickly overwhelm health systems and lead to high numbers of hospitalizations.

Brazilian health authorities decided to prioritize vaccination of adolescents between the ages of 10 and 14 because this age group accounts for a significant proportion of symptomatic cases and presents a considerable risk of hospitalization. Furthermore, this group is highly exposed to the mosquito that transmits the disease because they are highly mobile and spend much of their daily activity outdoors. Thus, a vaccination campaign was organized throughout the year, and nearly 690,000 doses of Qdenga were administered. According to the research findings, protection began fourteen days after the first dose, was maintained for the first three months, and subsequently declined.

Despite the positive results, the authors also point out some limitations that should be taken into account, such as the low vaccination coverage they achieved and the lack of information on the adolescents' prior immune status against dengue, so they do not know whether they had previously been infected. However, Ranzani insists that the study's results "will be fundamental" in guiding vaccination decisions in countries where the disease is endemic and frequently experience outbreaks. The expert maintains that a single dose already offers significant protection within a few weeks, making the vaccine a key tool for halting ongoing epidemics and reducing hospital burden.

Europe, waiting for dengue

Rising temperatures due to the climate crisis and the increase in international travelers, coupled with the proliferation of mosquitoes, create the perfect breeding ground for this disease to become increasingly prevalent in Europe, which is not yet a dengue-endemic region. Local outbreaks have already appeared in France, Italy, and also Catalonia, and cases imported by travelers are increasingly common. Between 2022 and 2024, more than 500 cases of imported dengue were reported in Catalonia, mainly in people who had traveled to endemic areas, and last year saw the largest outbreak of native dengue in Spain. Therefore, Ranzani maintains that having effective vaccines "can make the difference in responding to future outbreaks and protecting travelers," including in European countries, where the risk of transmission is increasingly high.