H3N2 flu strain: Global health authorities are tracking a newly emerged H3N2 influenza variant that surfaced in June, months after this season’s vaccine composition was set, and is now driving early outbreaks in parts of the Northern Hemisphere.
The strain has quickly become dominant in some countries, with Canada and the U.K. reporting rising hospitalisations and an unusually brisk start to flu season. “Since it emerged, it’s rapidly spreading and predominating in some countries so far in the Northern Hemisphere,” said Dr Wenqing Zhang, who leads the World Health Organization’s Global Respiratory Threats Unit.
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Scientists say the circulating H3N2 picked up seven additional mutations over the summer, making it “quite different” from the H3N2 component in this year’s vaccine, according to Antonia Ho, an infectious-diseases consultant at the University of Glasgow. U.K. health officials have warned of flu activity roughly triple last year’s level for this point in the season.
Elsewhere, Japan is reporting an “unprecedented” early and severe wave. By Nov. 4, Tokyo’s flu cases were nearly six times higher than at the same time last year, prompting partial closures at more than 2,300 schools and day-care centers, according to the health ministry.
In the US, anecdotal reports of influenza A are on the rise. Still, national, detailed surveillance has lagged amid a federal shutdown and broader staffing cuts that may slow data collection and analysis. Experts expect more reliance on state and academic laboratories in the near term.
Despite the mutation gap, vaccines still offer meaningful protection against severe disease. Last season, flu shots were up to 55% effective at preventing hospitalisation in adults; preliminary U.K. estimates this year suggest up to 40% effectiveness against hospitalisation among adults. “Even if there is not a close match, use of the vaccine continues to prevent hospitalisations, ICU admissions and deaths,” said Dr William Schaffner of Vanderbilt University Medical Centre.
This season’s Northern Hemisphere vaccines target three flu strains (two influenza A, one influenza B). While they do not fully prevent infection, health agencies continue to urge vaccination, especially for older adults and those with underlying conditions, along with standard precautions such as staying home when ill and seeking early antiviral treatment when appropriate.
