Flu: already 3.3 million in bed, young children most affected. Variant that resists antiviral emerges

Flu continues its rise in Italy with a higher incidence than last year's season, which still set an absolute record with 16.1 million Italians affected. Although it is not totally correct to make comparisons - also because this year's calculation uses different parameters - there is no doubt that the circulation of viruses has been growing steadily since the beginning of this season. In the last week, 585 thousand Italians have been put to bed by respiratory infections, including influenza. Since the beginning of the season, 3.3 million infections are estimated. The data emerges from the weekly report of the RespiVirNet surveillance system of the Istituto Superiore di Sanità. During the week between 24 and 30 November, 10.4 cases of respiratory infections per 1,000 inhabitants were recorded, an increase of around 11% compared to the previous week, when there were 8.96 cases per 1,000. Young children, between 0 and 4 years old, continue to be the most affected, with 33 cases per 1,000. Meanwhile, attention is growing for the spread of a variant of the common flu virus that is resistant to a common antiviral.

As mentioned, the total incidence of acute respiratory infections in the week from 24 to 30 November was 10.4 cases per 1,000 patients (compared to 8.96 in the previous bulletin), an increase compared to the previous week and 'as expected for the period'. The intensity is currently, however, 'low in almost all regions, while it is at baseline in Liguria, Molise, the province of Trento, and Umbria,' the bulletin points out. Which recalls how 'the change in the case definition', from influenza-like syndrome Ili to acute respiratory infection Ari (to more accurately monitor respiratory viruses other than influenza), 'makes it difficult to compare the current weekly incidence' 'with that of previous seasons, as well as with the intensity thresholds, calculated on the basis of data relating to influenza-like syndromes in recent seasons'. In any case, the signs coming from the first numbers of this virus season portend an advance on last year, with the possible peak of cases arriving as early as the end of December and January, in line with what happens in the 2023-2024 season, for example, while last year the peak of cases occurred later, towards the end of January.

But which viruses are affecting the most at the moment? According to the analyses contained in the report, the highest positive values were detected for influenza viruses, Rhinovirus and Sars-CoV-2, respectively. "In detail," explains the Iss, "during the week, 2,088 clinical samples received by the various laboratories belonging to the network were reported through the RespiVirNet portal, and from the analyses carried out 423 (20.3%) were positive for the influenza virus, in particular 421 type A and 2 influenza B. Of these analysed samples, 83 (4%) were positive for Sars-CoV-2, 51 (2%) for respiratory syncytial virus (Rsv) and the remainder were positive for other respiratory viruses: 275 (13.2%) rhinoviruses, 69 (3.3%) parainfluenza viruses, 56 (2.7%) adenoviruses, 37 human coronaviruses other than Sars-CoV-2, 16 bocaviruses and 6 metapneumoviruses'. To date, finally notes the Istituto Superiore di Sanità, no positive samples have been reported for influenza type A 'not subtypable' as seasonal influenza, which could be indicative of the circulation of avian strains.

"The figure for flu vaccination coverage" achieved so far in the current campaign "is not particularly exciting". This is the view of virologist Fabrizio Pregliasco, who analyses: "Certainly those who are 'habitués' of vaccination are getting vaccinated, but" even this year "we are not succeeding in breaking this sad division and this lack of conviction of the opportunity represented by immunisation. The current estimate, hopefully still not complete, indicates a 50% of the over-65s vaccinated, a quota that is in line with last year's, but still a bit lower since in the 2024-2025 season it had stopped at 53%, already declining in recent years if one considers the 63% or so reached in 2021, the year of Covid,' the expert recalls. Therefore, according to the virologist, the feelings of mistrust and scepticism towards the value of vaccination have not yet been shaken, 'especially if we look at the statistics on those most at risk, i.e. the over-65s, given also the comorbidities that are often present,' points out Pregliasco, director of the School of Specialisation in Hygiene and Preventive Medicine at the State University of Milan. "In conclusion, the data on influenza vaccination do not appear enthusiastic, and if we then go and look at the adherence to the anti-Covid vaccination" it gets even worse. 'We unfortunately see values that are definitely and sadly very low'.

Meanwhile, attention is growing for the spread of a variant of common flu viruses, characterised by a genetic mutation (S247N neuroamidase) that makes the antiviral drug oseltamivir less effective. A study co-ordinated by the Vall d'Hebron research institute in Barcelona and published in the journal of the European Centre for Disease Prevention and Control (Ecdc) showed that in Catalonia, 11.8% of the type A/H1N1 flu samples analysed since the start of the season possess this mutation, which has been known for fifteen years but had hitherto been very rare. A similar trend was observed in France, the Netherlands, Norway, Denmark and Belgium, and overall, 2.2% of European A/H1N1 sequences possess the mutation. When combined with other mutations, this alteration can make the virus completely resistant to antivirals. Therefore, "enhanced surveillance of the evolution of these influenza A/H1N1 virus strains" is urgently needed, say the researchers.