On Thursday, the Brazilian Health Ministry published data showing that the number of dengue cases has almost tripled since January due to the rains and high temperatures associated with the El Niño phenomenon.
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In the first three weeks of January, 120,874 cases were recorded, with an incidence rate of 59.5 per 100,000 inhabitants, a figure that exceeds the 44,753 cases recorded in the same period in 2023. It were also confirmed 12 deaths and 85 cases under investigation.
Health authorities expect between 1.7 and 5 million cases of dengue in 2024, which would set a record for this mosquito-transmitted disease. In 2023, Brazil recorded 1.6 million cases and over 1,000 deaths from dengue.
"Since mid-last year, the high temperatures caused by El Niño have been halving the mosquito's development time," said Tamara Nunes de Lima-Camara, associate professor of epidemiology at the Sao Paulo University.
Furthermore, the increase in temperatures has expanded the mosquito's distribution area. In Brazil, the number of dengue cases has increased even in the southern region, where the temperature is usually colder.
For example, between 2002 and 2023, the number of confirmed dengue cases increased from 436 to 38,657 in Rio Grande do Sul, a state bordering Uruguay and Argentina.
This is compounded by the reappearance of a dengue variant not seen in Sao Paulo for ten years, and for which the younger population is not immune due to lack of previous infection.
In response to this situation, major cities have begun to fumigate the streets with insecticides. The Sao Paulo Municipality purchased 30 vehicles for spraying and hired 700 officials to conduct house-to-house inspections.
"Control tools such as fumigation have not been sufficient. Records of cases continue to break year after year in Latin America. We need investment in science and technological innovations," said Julio Croda, who is an infectious disease specialist at the Oswaldo Cruz Foundation (FIOCRUZ) and president of the Brazilian Society of Tropical Medicine.
Among these innovations is the release of mosquitoes into which FIOCRUZ scientists had introduced a bacterium that reduces their ability to transmit dengue.
A study published in the Public Library of Science on the application of this practice in the city of Niteroi shows a 69 percent reduction in incidence three years after the program's launch.
Nevertheless, the most powerful weapon is vaccines. In 2024, Brazil plans to buy up to 6.2 million doses of a Japanese vaccine, which will be administered free of charge to children and adolescents starting in February. However, since immunization requires a double dose, this quantity only covers 3.1 million people.
To avoid dependence on foreign laboratories, the Butantan Institute in Sao Paulo is developing a single-dose vaccine, and clinical trials already point to an overall efficacy of 79 percent.