Atypical Respiratory Virus Season Overwhelms Brazilian Healthcare in 2025
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Brazil’s healthcare system faced an unprecedented challenge in 2025, grappling with an unusually intense and prolonged surge in severe acute respiratory syndromes (SARS), extending far beyond typical seasonal patterns. The strain led to widespread unpredictability and overwhelmed hospitals, forcing officials to re-evaluate traditional disease calendars and allocate significant resources to manage the crisis.
Data from InfoGripe, the Unified Health System (SUS) platform monitoring SARS cases nationwide, revealed alarmingly high rates of hospitalizations and deaths. A particularly striking development was the occurrence of two waves of influenza A within the same year, persisting through both spring and summer – a phenomenon rarely observed in Brazil. While Covid-19 continued to contribute to mortality, particularly among the elderly, other respiratory viruses simultaneously increased pressure on hospital capacity, especially impacting children.
“The challenge is broad because it is necessary to spend more money to carry out differential diagnoses,” explained an infectious disease specialist from Einstein Hospital Israelita. “We have a high hospitalization rate not only for influenza, but also for Covid-19 and respiratory syncytial virus (RSV). All of this overloads the healthcare system.”
By the end of 2025, Brazil had reported over 230,000 SARS cases, with just over half receiving laboratory confirmation for a specific respiratory virus, resulting in 13,678 deaths. RSV accounted for the largest proportion of positive cases, followed by rhinovirus and influenza A. However, influenza A was the leading cause of death, closely followed by Covid-19, which, despite a lower overall incidence, maintained a disproportionately high mortality rate.
A Year of Firsts and Shifting Dynamics
Researchers identified 2025 as an atypical year due to both the sheer intensity of influenza A cases – with a higher-than-usual number of severe infections – and the unexpected second wave of the virus. “We usually see a wave around April and May, but in 2025 there was a second wave in the spring and summer,” observed Tatiana Portella, a researcher from the Scientific Computing Program of the Oswaldo Cruz Foundation (Fiocruz) and InfoGripe.
In December, Fiocruz researchers detected, for the first time in Brazil, the K subclade of the influenza A (H3N2) virus. The case originated from a traveler arriving in Belém and was classified as imported, with no evidence of local transmission at the time. While the detection raised concerns due to the virus’s recent circulation in the Northern Hemisphere, officials emphasized it did not immediately signal a shift in Brazil’s influenza patterns. Current surveillance efforts remain focused on identifying the specific virus driving each SARS case, as their behaviors differ.
Specifically, influenza A historically poses the greatest mortality risk to the elderly, while RSV is the primary cause of severe hospitalizations in young children. Rhinovirus, traditionally associated with milder illness, increasingly appeared in severe cases, particularly among pediatric patients. Despite declining overall numbers, Covid-19 continued to exert a significant impact on mortality rates.
Early 2026 Shows Signs of Respite, But Vigilance Remains
The start of 2026 offered a glimmer of hope, with the InfoGripe bulletin for the first epidemiological week of the year, published on January 8, indicating a decline in both short- and long-term SARS case trends. Most of the country remained outside of alert levels, with the exception of the North region, where some states continued to experience increased hospitalizations due to influenza A, particularly among adults and the elderly, prompting a SARS alert on January 15th.
However, Portella cautioned against premature optimism, stating, “It is still too early to make consolidated projections about the behavior of these syndromes in 2026.” While models exist to predict disease trends, updated data is crucial for accurate risk assessment and effective vaccination planning. For influenza and RSV, an increase is generally expected in autumn and winter. Covid-19, however, remains less predictable due to its lack of strict seasonality and reliance on the emergence of new variants.
The Role of Seasonality and Vaccination
Unlike influenza and RSV, which typically peak during autumn and winter, Sars-CoV-2, the virus causing Covid-19, exhibits a less predictable pattern, with increases often linked to the emergence of new variants. A prolonged cold period in many regions of Brazil may have also contributed to the extended rise in influenza cases.
These factors collectively redefined the dynamics of severe respiratory diseases in Brazil and placed considerable strain on the healthcare system. In total, 2025 saw 120,176 hospitalizations for SARS. The Ministry of Health responded by allocating R$100 million to municipalities for pediatric care and R$50 million for adult patients. “This situation catches health systems off guard. We don’t expect to see a rise in hospitalizations due to flu, for example, in the spring or summer. So, all of this affects the population and the health system,” Portella emphasized.
A significant contributing factor to the crisis was low vaccination rates, particularly against the flu. “The chronic problem is vaccination. We know that adherence is lower than expected, which favors the circulation of these viruses,” noted the infectious disease specialist at Einstein. The atypical seasons of the H1N1 and H3N2 viruses further exacerbated the situation. While the available influenza vaccine protects against circulating strains, the two distinct seasons contributed to two waves of infection.
Influenza vaccination coverage among priority groups during the mid-year campaign reached only 53.43%, according to the Ministry of Health – insufficient to significantly reduce hospitalizations and deaths. Covid-19 vaccination coverage was even lower, at just 3.49%. This incomplete protection facilitated the prolonged circulation of viruses and the occurrence of successive waves throughout the year.
Preventive measures, including staying up-to-date on vaccinations, practicing respiratory etiquette, avoiding travel while symptomatic, and wearing masks in high-risk environments, remain critical for mitigating transmission and impact. “People stopped adopting basic precautions, such as respiratory etiquette and using alcohol gel. I don’t think we learned much from the pandemic [de Covid-19]. On the contrary, we forgot,” lamented the doctor from Einstein.
