Flu Season Arrives Early in Portugal, driven by Influenza A
Flu activity is rising in Portugal, arriving three to four weeks earlier than usual and mirroring the 2023-24 season’s pattern. Recent data from the Sentinel doctors Network shows a rise in laboratory-confirmed influenza cases over the past two to three weeks. The incidence of severe acute respiratory infections increased to 10.5 cases per 100,000 inhabitants during the week of November 24th-30th, with the highest increases observed in children under five and adults over 65.
Currently, 82 serious cases are hospitalized, with 10 in intensive care. A majority of those hospitalized had underlying chronic conditions and were recommended to receive a flu vaccine (though only three had been vaccinated). Influenza accounts for 6.0% of ICU cases, up from 1.6% the previous week.
The circulating strains are primarily Influenza A,with both AH1N1 and AH3N2 subtypes present,currently with a slight dominance of AH1N1. However, a new subgroup of AH3N2, designated K, is gaining traction, representing 45% of characterized AH3N2 viruses in Portugal. This variant has evolved with mutations possibly increasing its transmissibility and is distinct from viruses covered by the 2025-2026 vaccine. Experts note that in other European countries experiencing an early season, this AH3N2-K variant saw a surge in circulation as flu activity began.
While the flu epidemic is still trending upwards and hasn’t reached peak activity, circulation of SARS-CoV-2 remains low and RSV activity is currently mild, though a future increase is absolutely possible. Researchers emphasize that disease severity is often linked to both the circulating virus and individual patient health conditions.
