Flu alert, early peak: Campania hospitals under pressure. H3N2 virus strikes unvaccinated people.

Seasonal influenza has reached very high intensity in Sicily and high in Campania, signaling an early and aggressive peak.

The latest national Influnet bulletin, covering week 51 (December 16-22), paints a picture of marked acceleration, with average viral circulation in much of central and northern Italy and the south, including Piedmont, Emilia-Romagna, Tuscany, Marche, Lazio, Abruzzo, Umbria, and Puglia. Other regions, however, are recording low levels.

The virus is putting a strain on the healthcare system: one in two patients with respiratory infections admitted to hospital has tested positive for influenza (50,3%), while the positivity rate in the community, as detected by family doctors, is 22,2%.

Monitoring of severe cases confirms the worrying trend: in week 51, there was an increase in cases compared to the same period of the previous season. The predominant viral subtype in the most severe cases is A(H3N2), and one finding is particularly significant: most of those affected by severe influenza or complications were not vaccinated.

Analysis of circulating viruses shows a clear prevalence of the A(H3N2) type both in the community and in hospitals, compared to the other A(H1N1)pdm09 strain. Sequencing analyses reveal that, among H3N2 viruses, the K subclade is clearly prevalent, while all H1N1 strains belong to the D.3.1 subclade.

The latter falls into the same broad group (clade 5a.2a.1) as the strains contained in seasonal vaccines, indicating a good match between the circulating virus and the protection offered by immunization.

A reassuring fact is the current lack of reports of "non-subtypeable" influenza A viruses, which could suggest the circulation of avian strains in humans. However, the health authorities' recommendation remains high, especially for at-risk groups, given the impact on hospitals and the vulnerability highlighted among the unvaccinated.