According to the researcher, in the last two to three weeks, there has been “an increase in the number of laboratory-confirmed cases of influenza virus infection” reported by the Sentinel Doctors Network.
The Insa Epidemiological Surveillance Bulletin for Flu and other Respiratory Viruses, released this Friday, reveals that in the week of November 24th to 30th there was an increase in the incidence rate of severe acute respiratory infections compared to previous weeks, reaching 10.5 cases per 100,000 inhabitants.
The age groups from zero to four years old and 65 years old and over were those that showed the greatest increase, with the latter showing the highest value.
This week, 82 serious cases of acute respiratory infection were admitted to the Local Health Units (ULS) that reported data, with 10 admissions to intensive care units (ICU) reported.
“All cases had an underlying chronic disease and a recommendation for vaccination against seasonal flu, three of which were vaccinated. This week, the proportion of influenza in ICU was 6.0%, having increased compared to the previous week (1.6%)”, states the bulletin.
Raquel Guiomar explained that, normally, the severity of the disease can be associated with the virus that is circulating, but often also with the individual conditions of each patient.
Regarding the viruses that are in circulation, the researcher stated that the viruses that infect the human population are of two types, A and B, and at this time essentially those of the influenza A virus are circulating.
“We have been detecting the two subtypes of the type A flu virus, either the AH1N1 virus or the AH3N2 virus”, with there currently being “a slight predominance” of AH1N1.
However, he stressed, the co-circulation of the two subtypes of the influenza A virus may change in the coming weeks.
Raquel Guiomar said that, in recent weeks, the AH3N2 subtype has received greater attention at national and international level, explaining that this virus, which circulated in the northern hemisphere last season and also in the southern hemisphere, evolved and acquired mutations that could increase its transmission and infection capacity.
These mutations distinguish it from viruses from the previous season and from those included in the 2025-2026 vaccine.
According to the researcher, the new subgroup of viruses of the AH3N2 subtype, designated K, has already been detected in Portugal and represents around 45% of the AH3N2 viruses characterized so far.
Asked if it tends to grow in the coming weeks, she stated that it is a hypothesis that could happen, given its characteristics, noting, citing European data, that in countries that had an earlier season than that observed in Portugal, these were the viruses that had an increase in circulation as soon as flu activity began.
The expert also said that the epidemic arrived “three to four weeks earlier” than usual in Portugal, approaching the pattern observed in 2023-24.
“But we have not yet reached maximum activity. Basically, we are, at the moment, experiencing epidemic flu activity with an increasing trend”, he stressed.
As for other respiratory viruses, the circulation of SARS-CoV-2 is currently reduced and respiratory syncytial virus (RSV) maintains low activity, although it may increase in the coming weeks.