“`html
Portugal Declares Flu Epidemic as Cases Surge, New Viral Strain Emerges
Portugal is currently experiencing an influenza epidemic with a concerning upward trend, marked by a rise in confirmed cases and increasing hospitalizations, including admissions to intensive care units. The warning was issued by the Doctor Ricardo Jorge National Institute of Health (INSA) on Thursday, December 5, 2025.
early and Increasing Activity
“The data relating to flu activity in this 2025-26 season showed that in week 48, which began on November 24, flu activity is epidemic,” explained Raquel guiomar, head of the National reference Laboratory for the Flu Virus and Other Respiratory Viruses at INSA. According to the researcher, a notable increase in laboratory-confirmed influenza virus infections has been reported by the Sentinel Doctors Network over the past two to three weeks.
The INSAS latest Epidemiological Surveillance bulletin, released today, December 6, 2025, indicates a heightened incidence rate of severe acute respiratory infections during the week of November 24th to 30th, reaching 10.5 cases per 100,000 inhabitants – a significant increase compared to previous weeks.
Vulnerable Populations at Risk
The most substantial increases in infection rates are being observed among children aged zero to four years and older adults aged 65 and over, with the latter group experiencing the highest rates.This week alone, 82 individuals with serious acute respiratory infections were admitted to Local Health Units (ULS), with 10 requiring intensive care.
A concerning trend highlighted in the bulletin is that all patients admitted to ICU had underlying chronic conditions and were recommended to recieve the seasonal flu vaccine, though only three had been vaccinated.The proportion of influenza cases in ICU has risen to 6.0% this week,up from 1.6% the previous week.
viral Landscape and Emerging strain
Guiomar emphasized that the severity of the illness is often linked to both the circulating virus and the individual health status of each patient. Currently, influenza A viruses are dominant, with two subtypes – AH1N1 and AH3N2 – circulating within the population. While AH1N1 currently holds a slight edge in prevalence, the situation is dynamic.
Of particular concern is the recent evolution of the AH3N2 subtype. This virus, which circulated in both the Northern and southern Hemispheres last season, has acquired mutations that may enhance its transmissibility and infection capacity. These mutations differentiate it from previous strains and from those included in the 2025-2026 influenza vaccine.
A new subgroup of the AH3N2 virus, designated K, has been detected in portugal and currently accounts for approximately 45% of characterized AH3N2 viruses. Experts are monitoring this strain closely, as data from other European countries suggest it may become dominant as flu activity intensifies. A chart illustrating the proportion of AH3N2-K versus other AH3N2 subtypes over time would be beneficial here.
Early Season and Future Outlook
The current epidemic arrived “three to four weeks earlier” than typically observed in Portugal, mirroring the pattern seen in the 2023-24 season. However, officials stress that peak flu activity has
