Europe may face a challenging flu season as the emergence of a new strain has raised alarm bells. This strain, responsible for early recorded increases in cases in the U.S., Canada, and Japan, belongs to subclade K of H3N2, a type of influenza A that circulates alongside B strains.
The subclade K had limited presence when the WHO selected the strains for this year’s vaccine, which appears to have somewhat reduced the effectiveness of vaccination, according to early data published from the United Kingdom.
In Greece, the latest report from EODY indicates that subtype A(H1)pdm09 is predominant, which includes subclade K, although it remains unclear whether this is the strain spreading in the country.
Early estimates from the UK Health Security Agency suggest that subclade K carries seven significant mutations in the hemagglutinin gene, the protein that enables the virus to infect human cells. Vaccines are proving less effective against it but still reduce severe illness: they prevent hospitalization by 75% for children and 30-40% for adults. Protection may wane as the seasonal epidemic progresses.
Despite the reduced effectiveness, vaccination remains the safest defense, especially since strains—such as those of influenza B—are more comprehensively covered by available vaccines.
To predict the trajectory of flu in the Northern Hemisphere, experts are examining its behavior in the Southern Hemisphere. In Australia, where subclade K dominated, over 443,000 cases were recorded, with virologist Richard Webby emphasizing that H3N2 strains typically pose greater challenges.
In the U.S., although flu activity remains low for now, it is rapidly increasing according to the CDC. This situation, combined with Australia’s experience, raises concerns among experts like Earl Rubin from Montreal Children’s Hospital, who warns that even without increased pathogenicity, the rise in cases will lead to more hospitalizations.
