The United States could be heading into a second consecutive severe flu season, fuelled by a mutated strain known as subclade K, which has already driven early surges in the United Kingdom, Canada and Japan.
Last winter’s flu was particularly severe, marking the highest US flu hospitalization rate in nearly 15 years. At least 280 children died—the most recorded since reporting became mandatory in 2004.
Experts warn that this season may mirror last year, with the added risk of the new variant spreading as vaccination rates decline and the holiday travel season approaches.
Flu activity remains relatively low but is rapidly increasing, according to the latest FluView data from the US Centers for Disease Control and Prevention (CDC).
Most detected flu viruses are an A-type strain, H3N2, with nearly half stemming from the emerging subclade K—the same variant linked to an unusually severe flu season in the Southern Hemisphere earlier this year.
Because this mutation was not widespread when flu vaccines were formulated, current shots target a slightly different strain.
Early analysis by the UK Health Security Agency indicates the vaccines provide strong protection for children (nearly 75% reduction in hospital or emergency visits), but lower protection for adults, around 30% to 40%. These results are preliminary and from early in the season.
Flu vaccinations in the US are lower than usual. Retail pharmacies administered about 26.5 million flu shots between August and October, more than 2 million fewer than during the same period last year.
Dr. Jennifer Nuzzo of Brown University attributed the decline to misinformation and public skepticism fueled by recent health policy debates.
Australia experienced a record 443,000 flu cases this year as vaccinations dropped, which experts warn could signal what lies ahead for North America.
Flu test positivity rose from under 1% to 2.4% earlier this month, mirroring trends seen in other countries. Wastewater monitoring also shows a jump from 18% to 40% in influenza presence across US sites.
With holiday travel approaching, clinicians predict accelerating transmission.
