Drazen Zigic / freepik
In the last two to three weeks, “an increase in the number of laboratory-confirmed cases of influenza virus infection” has been observed.
Portugal entered influenza epidemic phase with increasing trendregistering an increase in cases confirmed, including hospitalizations in intensive care, warned the Doctor Ricardo Jorge National Institute of Health (INSA) today.
“Data relating to flu activity in this 2025-26 season (…) showed that in week 48, which began on November 24, flu activity is epidemic”, Raquel Guiomar, responsible for the National Reference Laboratory for the Influenza Virus and Other Respiratory Viruses at Insa, told Lusa.
According to the researcher, in the last two to three weeks“a increase of the number of laboratory-confirmed cases of influenza virus infection” and reported by the Sentinel Doctors Network.
The Insa Epidemiological Surveillance Bulletin for Flu and other Respiratory Viruses, released today, reveals that in week of November 24th to 30th an increase in the incidence rate of severe acute respiratory infections was observed compared to previous weeks, reaching 10.5 cases per 100,000 inhabitants.
The age groups of zero to four years old and from 65 years old or more were those that showed the biggest increase, with the latter showing the highest value.
This week, they were admitted 82 serious cases of acute respiratory infection in 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 virus that is circulating, but often also at 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 e Band at this time the virus is essentially circulating influenza A.
“We have been detecting the two subtypes of the type A flu virus, either the AH1N1 virus or the AH3N2 virus”, and there is currently “a slight predominance” of AH1N1.
However, he highlighted, 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 subtype AH3N2 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, called K, has already been detected in Portugal and represents around 45% of the AH3N2 viruses characterized so far.
Asked if tends to grow in the coming weeksstated 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” than usual in Portugal, approaching the pattern observed in 2023-24.
“But we have not yet reached maximum activity. Basically, We are currently 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.
