El Niño raises alert for dengue in 2027; projection points to a chance of 866 thousand cases

Aedes aegypti, the mosquito that transmits dengue fever, has a great capacity for adaptation. — Photo: CDC

The super El Niño predicted for the summer could increase the risk of dengue fever in some regions of Brazil in 2027, but there is still a lot of uncertainty about the size of this effect, according to new projections presented this past Friday (6) by the Oswaldo Cruz Foundation (Fiocruz).

The main estimate points to around 866 thousand probable cases of dengue in the country in the next season, in a scenario considered similar to that of 2025 and 2026.

This number, however, does not directly take into account the possible effects of El Niño.

The researchers separately tested models that include climate variables. And the results did not reach the same conclusion: some project more cases in certain regions, while others indicate a smaller impact.

In the South, models that consider El Niño more consistently point to a longer dengue season than indicated by the main projection. In other regions, the picture is more uncertain.

🌡️ UNDERSTAND: El Niño is characterized by the abnormal warming of the waters of the Equatorial Pacific Ocean and changes rainfall and temperature patterns in different parts of Brazil.

Heat and humidity can favor the reproduction of Aedes aegypti, a mosquito that transmits dengue, zika and chikungunya, but the effect on cases also depends on local conditions, the susceptible population and control actions.

Therefore, the researchers state that the phenomenon should act as a warning sign for planning, and not as a basis for calculating alone how many cases there will be in the country.

The projection brings together 22 models developed by more than 130 researchers from eight countries. Instead of choosing just one of them, scientists combine the results to arrive at an estimate that is considered more robust.

For 2027, this combination points to around 860 thousand cases, but with a very wide range: there is an 80% probability that the total will be between approximately 560 thousand and 1.6 million.

The peak is expected in April, with around 40,000 cases in one week.

Although the forecast does not indicate an epidemic like that of 2024, the researchers emphasize that this does not mean a calm year.

"Dengue will continue to demand attention. It is time to organize the network and intensify prevention", said Claudia Codeço, researcher at Fiocruz and coordinator of InfoDengue, in a statement.

The models also point to an increasing trend in cases compared to the previous season in Paraná, Rio de Janeiro, Mato Grosso do Sul, Sergipe, Acre and Minas Gerais.

In other states, the projection is for a scenario close to or below that recorded in the previous season.

Still, researchers recommend maintaining vigilance across the country precisely because El Niño could change weather conditions over the next few months.

The team also made, for the first time, a national projection for chikungunya, a disease transmitted by the same mosquito.

The estimate points to more than 90 thousand probable cases in 2027, with an increasing trend mainly in the Northeast, South, São Paulo, Mato Grosso and Mato Grosso do Sul.

Dengue: see what the disease is and what its symptoms are — Photo: Arte g1/Dhara Assis