NEW YORK — The U.S. flu season is off to a slow start, but health experts are expressing new concern as Centers for Disease Control and Prevention (CDC) data released shows a newly emerged version of the virus driving recent infections.

Early analysis suggests current flu vaccines may still offer some protection against the new strain, which is part of the type A H3N2 family — historically linked to higher hospitalization and death rates, particularly among older adults.

Some scientists worry more about lagging vaccination rates, which contributed to one of the deadliest flu seasons in decades last winter.

“I think we’re going to see a really severe season,” said Asefeh Faraz Covelli of the George Washington University School of Nursing.

Last year’s flu hospitalization rate was the highest since the 2009 H1N1 pandemic. More than 18,000 deaths were attributed to the flu, including an early-year spike of more than 1,800 fatalities in a single week — the highest weekly toll in at least ten years. Pediatric flu deaths were also well above average.

So far this season, flu activity remains low nationwide, with only Louisiana reporting moderate levels, according to CDC influenza surveillance lead Alicia Budd.

Most infections are appearing in children and are linked to a new H3N2 subclade — known as variant K — which differs from the strain targeted in this year’s flu shot.

A preliminary study from the United Kingdom suggests the current vaccines still provide at least partial protection, though researchers say more data is needed.

Flu cases typically rise sharply between December and February, and officials expect an uptick as Americans travel and gather for Thanksgiving.

“This is the ideal time to get vaccinated,” Covelli said.

The CDC’s ability to track respiratory trends has been challenged by a recent government shutdown that briefly halted data collection just as seasonal infections began climbing.

At the same time, U.S. vaccine messaging has grown more limited since Health Secretary Robert F. Kennedy Jr. — a longtime vaccine critic — took charge of the CDC and other federal health agencies. His statements questioning vaccine safety have injected new uncertainty into public health campaigns.

COVID-19 vaccination rates have continued to drop, with only about 6% of children and 14% of adults up to date — several points lower than last fall.

Flu vaccination trends are mixed: pharmacy-administered flu shots are down by more than two million compared to this time last year, according to IQVIA, but CDC survey data shows steady childhood vaccination rates at 34% and a slight increase among adults to 37%.

It remains too early to know whether the upward trend will continue, CDC officials said.

As of early November, the U.S. flu hospitalization rate is roughly on pace with the same period last year. COVID-19 and RSV hospitalization rates remain lower than in the previous season, according to the CDC. — Agencies