In 2024, Brazil counted more than 6,000 deaths from dengue fever and 2025 is expected to be even worse, according to an article in a major Brazilian media outlet1. There are several reasons for this sharp increase, starting with global warming and heavy rainfall. Dengue is a viral disease transmitted by mosquitoes. There are several effective methods of preventing the disease, starting with vaccination.
Latin America and especially Brazil
In 2023, around 80% of confirmed cases of dengue in the world occurred in Latin America and its 670 million inhabitants. In 2025, the state of Sao Paulo (the most populous in Brazil) had 116,550 probable cases of dengue during the first 5 weeks of that year, with 25 confirmed deaths already 2. In recent years, dengue fever has also affected countries with a generally cooler or drier climate, such as Chile and Uruguay, according to The Economist.
Virus that bites during the day
Dengue fever is transmitted by the bite of a mosquito – Aedes aegypti – infected with the virus. The mosquito lives and bites during the day. It transmits the viruses through its saliva when it bites the human skin, and the viruses then multiply in the human blood. Symptoms will appear in approximately 40 to 50% of people infected by the dengue virus. In other words, 50 to 60% of people bitten by a mosquito carrying the virus will not show any symptoms (asymptomatic).
4 or 5 serotypes of the virus
The dengue virus has 5 serotypes or strains: DEN1, DEN2, DEN3, DEN4 and DEN5. Some sources or medical authorities speak of 4 serotypes. It is not possible to be infected a second time by the same serotype. The WHO warns that all four serotypes of the disease were detected on the American continent in 20243. But a person can be infected by one of the (three or) four other serotypes. For example, one can be infected by DEN1, then a few weeks, months or years later by DEN2, 3 or 4 or 5. But in this example the same patient cannot be infected twice in their life by DEN1.
5% in hospital
Dengue is not always without serious consequences, with around 5% of those infected requiring treatment in hospital. Some patients can develop a severe form of the disease called dengue hemorrhagic fever, which can be fatal. Every year around the world, around 40,000 people die from dengue. This figure has risen sharply in recent decades, according to The Economist. In the case of hemorrhagic dengue, the symptoms of classic dengue are present, but bleeding occurs after the fever subsides. In the case of hemorrhagic dengue, great care is required and therefore a doctor should be consulted immediately in the case of intense abdominal pain, cyanosis or spontaneous bleeding.
Not just the climate
Even if global warming and heavy rainfall, such as in southern Brazil, seem to explain a large part of the increase in cases, it should be noted that the urbanization of Latin America, with large cities such as Sao Paulo, Buenos Aires, Rio de Janeiro, Santiago de Chile, Mexico City and Lima, often with large suburban housing estates as well as favelas, does not help to reduce the number of mosquitoes. Mosquitoes thrive in the stagnant water that can be found in these neighborhoods, which is why there are more infections in the suburbs than in the city center, which has fewer water sources. Standing water can be found in vases, pots, holes in the road or garden, swimming pools or on flat roofs (water accumulates and can form small pools). In Brazil, medium-sized cities in the state of Sao Paulo with a hot and humid climate (north of the state) are particularly affected, such as Araçatuba or São José do Rio Preto. In Brazil, serotype 3 (DEN3) is currently circulating widely. For decades, this serotype was not transmitted by mosquitoes. This results in a higher death rate as this strain of the virus infects people already infected with another serotype (e.g. 1, 2, 4 or 5) but who have never been in contact with DEN3.
Vaccines
There are several vaccines on the market to prevent dengue. One is called QDenga® (or Qdengua®), and is indicated in the European Union for the prevention of dengue in people aged 4 years or older (in Brazil the vaccine is registered for people aged 4 to 60 years4. This vaccine contains live attenuated dengue viruses5. However, this vaccine is not produced on a large scale and is not available throughout Latin America. At least one vaccine project is at an advanced stage of clinical study. Sanofi’s Dengvaxia® vaccine is also available but can be dangerous for people who have never had dengue fever. In Brazil, according to Anvisa (the regulatory agency), the package insert for Dengvaxia® stated in January 2022 that Dengvaxia® should be administered to adults, adolescents and children aged 9 to 45 who have already been infected with dengue and live in endemic areas.
On May 10, 2024, the WHO prequalified a dengue vaccine, TAK-003, manufactured by the Japanese pharmaceutical group Takeda. It combines weakened components of four serotypes of the virus that causes this disease. The WHO recommends its use in children aged 6 to 16 in environments with a high prevalence and spread of dengue. The vaccine must be administered in two doses with a three-month break between them. It can now be used by UN agencies in their efforts.
Other means of prevention
Another means of prevention developed on a large scale, particularly in Singapore, consists of injecting bacteria called Wolbachia into the eggs of mosquitoes before releasing them into the wild. With this method, the mosquitoes are less likely to carry the virus that causes dengue fever, reducing the number of cases of infection by around 75%. Singapore releases 5 million mosquitoes with these bacteria every week. But this method is expensive, probably too costly for the economic situation in Latin America. In this region of the American continent, the best means of prevention is to alert the population never to have stagnant water. The health authorities often carry out general or targeted information campaigns. In particular, it is advisable to put sand in the saucers of plant pots, turn bottles upside down, cover water tanks and swimming pools (or add chlorine) and avoid storing tires outside.
February 10, 2025. By Xavier Gruffat (pharmacist).
- O Estado de S.Paulo newspaper, February 10, 2025 print edition
- O Estado de S.Paulo newspaper, paper edition of February 10, 2025
- O Estado de S.Paulo newspaper, paper edition of June 4, 2024
- O Estado de S.Paulo newspaper, paper edition of February 10, 2025
- Pharmavista.ch, Dengue : vaccin tétravalent autorisé, December 21, 2022
