The document describes the clinical and laboratory characterization of flu activity, integrating clinical and laboratory surveillance, with enhanced monitoring of other respiratory viruses such as SARS-CoV-2, respiratory syncytial virus (RSV), coronaviruses, and enteroviruses. Activities are carried out by INSA's National Reference Laboratory for Influenza Virus and Other Respiratory Viruses, in collaboration with the Directorate-General of Health and sentinel networks of doctors and laboratories.
In the 2025/2026 season, there was an early circulation of the flu virus in October 2025, with the epidemic period occurring in December 2025 and January 2026. Influenza A subtypes A(H3N2) and A(H1N1)pdm09 were detected, with the B flu virus detected sporadically. A new variant of A(H3N2) belonging to subclade K was identified, distinct from the viruses in the 2025/2026 vaccine.
The A(H3N2) and A(H1N1)pdm09 viruses showed antigenic and genetic characteristics similar to the viruses in the vaccine recommended for the 2026/2027 season. The most frequent respiratory viruses were rhinovirus, RSV, adenovirus, and metapneumovirus, with higher detection in children aged 0-14 and adults over 65.
The report indicates a period of excess mortality between weeks 49/2025 and 05/2026, primarily affecting the age group over 85 years. Patients admitted to Intensive Care Units (ICU) were often 55 years or older, with underlying chronic conditions such as cardiovascular disease, obesity, diabetes, and chronic obstructive pulmonary disease.
The A(H5N1) influenza virus is considered a threat, although no human cases have been detected in Portugal yet. The report's findings are considered useful for planning prevention and control measures for respiratory viruses.
