In Brazil, cases and deaths from RSV (respiratory syncytial virus) — the main cause of bronchiolitis — increased by 61.4% and 64.6%, respectively, from January to October 20, 2025, compared to the same period in 2024. The data are from the Ministry of Health. Experts interviewed by the report attribute the increase to this year’s “long winter.”
It is worth noting that the agency has not updated outstanding notifications from 2024 since last June. Although the initial compulsory notification has a defined deadline to be made, which depends on the condition, the epidemiological investigation phase can be time-consuming.
Bronchiolitis is an acute respiratory disease that mainly affects children under two years of age. It is characterized by inflammation of the bronchioles, small airways in the lungs.
“Climate change affects the presence of respiratory viruses. Everything that causes us to have more clusters of people, a reduction in ciliary movement, which is a defense of the lungs — lower temperatures do this —, promotes greater spread of viruses. This is the case with current conditions. Last year was hotter”, explains Marcelo Otsuka, pediatrician and infectious disease specialist at the Brazilian societies of Pediatrics and Infectious Diseases.
“This virus is easy to transmit and therefore has a very marked characteristic of seasonality, that is, in the colder months cases increase. As we had the most severe winter and we still have low temperatures, it undoubtedly makes it easier. Another aspect is that we are more attentive to the virus and carrying out more diagnoses. I think it is the sum of two things”, explains Evaldo Stanislau de Araújo, infectious disease specialist at Hospital das Clínicas de São Paulo.
According to data from the State Department of Health, São Paulo follows the country’s trend. When comparing January to October 25 of this year with the same period in 2024, cases of syncytial virus increased by 60.03%, and deaths, by 59.2%.
Young children account for the majority of RSV infections. In 2024, of the 26,285 cases that occurred in Brazil until October, 22,282 were in children under two years of age and 2,035 in those aged two to four years.
In 2025, of the 42,450 infections, 34,988 were registered in children under two years of age and 3,620 in children aged two to four years.
For every five children infected with RSV, one requires outpatient care and, on average, one in every 50 is hospitalized in the first year of life. In Brazil, around 20 thousand babies under one year old are hospitalized annually. The information is from the Ministry of Health.
In the SUS (Unified Health System), there is still no vaccine against RSV for children. According to the Ministry of Health, the vaccine will be offered from the second half of November. Pregnant women should be vaccinated from the 28th week onwards. The vaccine, administered in a single dose, will offer protection to newborns in the first months of life.
The monoclonal antibody nirsevimab, indicated to protect premature babies under 37 weeks and children up to two years of age born with comorbidities against RSV, will also be incorporated into the SUS. The medication, which prevents the virus from entering cells, reducing the risk of serious infection, will be dispensed in maternity wards. The forecast is February 2026.
Protection against the disease also consists of avoiding contact with other people if an infectious condition is suspected.
“If I have flu symptoms, I won’t go near an elderly person, a small child, especially a newborn, because he could have a serious condition if he catches my infection. So, I won’t go near people who are susceptible to having serious conditions. Likewise, a child who has the flu, which could be bronchiolitis, should not be taken to daycare. Protecting others, good hygiene, such as washing your hands, wearing a mask and not kissing children if you have the flu are other measures to take be adopted”, says Marcelo Otsuka.
RSV also causes pneumonia and serious conditions in the elderly. “It increases the possibility of decompensation of pre-existing diseases, such as diabetes and hypertension, and the chance of heart attack and stroke, just as influenza and coronavirus can also cause”, says Otsuka.
Prolonged winter and low vaccination coverage impact flu numbers
In 2025, from January to October 18, flu cases —caused by the influenza virus— rose 79.7% compared to the same period the previous year. In deaths, the increase was 99.1%.
The increase is reflected in the state of São Paulo, which registered an increase of 73.9% in cases and 97.1% in deaths, when comparing the periods from January to October 25, 2024 and 2025.
As with RSV, the extension of cold days increases flu cases, but it is not the only reason. Vaccination coverage remains far from the target, which is 90%.
In the Northeast, Central-West, South and Southeast regions of Brazil, in 2025, flu vaccination coverage among the public included in the routine strategy – people over 60 years old, children aged six months to under six years old and pregnant women – is 50.51%, according to the Ministry of Health. In the North of the country it reached 58.13%.
In the state of São Paulo, coverage is 51.68%, according to the agency’s influenza panel. The goal is to reach 90%.
“Another problem is that Brazil is a country of continental dimensions. We start from a simplistic premise that what happens in the Northern Hemisphere happens in Brazil, so the vaccine that was good in the Northern Hemisphere will be good for Brazil, but not necessarily we can have different strains of the influenza virus concomitantly occurring in Brazil in different territories. So, the flu virus in the south will almost always be different from the flu virus in the north. And then you start to have a vaccine that is not as effective as it could be. We need vaccines with more precision”, says Evaldo.
Influenza is an infectious and transmissible respiratory disease. Symptoms are runny nose, fever, headache and body pain, cough and malaise. The disease can be mild, lasting three to five days, or severe. It is not possible to know in advance how the patient will progress.
The doctor also draws attention to the circulation of bacterial diseases and the importance of protecting oneself against pneumococcal bacteria, which can cause pneumonia, meningitis and bacteremia (generalized blood infection), and milder infections, such as otitis.
The SUS offers the 13-valent pneumococcal conjugate (VPC13) and 23-valent pneumococcal polysaccharide (VPP23) vaccines to protect the elderly and adults with comorbidities, according to specific criteria. The vaccination schedule depends on the patient’s age, health status and vaccination history.
“Protecting against respiratory infections, respiratory syncytial virus, influenza, coronavirus, pneumonia and invasive pneumococcal disease improves indicators of heart disease”, says the HC infectious disease specialist.
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