Flu cases rise across US as holiday travel fuels spread

Summary

• US flu cases are rising rapidly due to holiday travel and low vaccination rates, with over 7.5 million illnesses reported.
• The dominant strain is influenza A(H3N2) subclade K, which shows mutations that evade some population immunity.
• Experts urge vaccination despite a slight mismatch with the virus, as it still offers protection, and to prevent further spread.

WASHINGTON - Flu cases are climbing across the US amid holiday travel and gatherings, with infections rising faster than in previous years, according to latest data from the Centres for Disease Control and Prevention.

Estimates released on Dec 30 showed at least 7.5 million illnesses, 81,000 hospitalisations and 3,100 deaths so far this season, while experts warned the numbers are likely to keep rising.

Holiday travel, low vaccination rates and misinformation are contributing to the spike, public health experts told Reuters.

Among 275 viruses collected since Sept 28, 2025, which underwent additional genetic characterisation at the CDC, 89.5 per cent belonged to subclade K, a variant of the influenza A(H3N2) virus.

A big concerning factor of this year’s flu season is how rapidly cases occur once influenza virus enters a certain state or geographic area, said Dr Andrew Pekosz, a virologist at Johns Hopkins Bloomberg School of Public Health.

Some experimental data and genetic sequence also shows that the virus seems to have some mutations that will avoid some of the population immunity, he said.

More than 19,000 patients with influenza were admitted to hospitals in the week ended Dec 20, up about 10,000 from the previous week, according to the CDC.

Five flu-related pediatric deaths were reported last week, bringing the total for the 2025-26 season to eight.

“This could be a much bigger flu season than what we’ve seen in the last several years, but so far we don’t have evidence that on a per-patient basis it’s more severe,” said Dr Daniel Kuritzkes, a senior Infectious disease physician for Mass General Brigham.

While severity indicators remain low, flu activity is expected to continue for several weeks, the CDC report said.

The agency urged anyone six months and older who has not yet received a flu shot to get vaccinated.

Experts also said while there is a mismatch between the vaccine and virus strains, people should get vaccinated, which will induce some antibodies that recognise the new variant and help fight off the disease.

“We know that the vaccine is not a perfect match to this strain... because the flu virus has mutated a little,” said Dr Eric Ascher, a family medicine physician at Northwell’s Lenox Hill Hospital.

About 130 million doses of influenza vaccine have been distributed in the country this season, the CDC said.

“All the holiday mingling is bound to increase transmission, and we have yet to see the start of a decreased acceleration in cases,” said Professor Cameron Wolfe, of Duke University. REUTERS