Flu is surging across the United States amid a busy holiday travel time.

The state of New York is among those most heavily hit. For the week ending Dec. 20, the state of New York reported its highest number of positive flu cases (71,123) ever recorded in a single week, according to the New York State Department of Health. That represented an increase of 38% over the previous week, the department said.

New York is one of 14 states that have reported high or very high activity of outpatient visits to healthcare providers for influenza-like illnesses, for the week ending Dec. 13, according to the Centers for Disease Control and Prevention. The District of Columbia, New York City and Puerto Rico have also registered high or very high flu-like cases, the agency says.

As of Dec. 16, flu infections were on the rise, or likely growing, in 47 states, with cases only declining in Hawaii, the CDC projected.

The increase in seasonal flu activity across the United States is similar to several past seasons, the CDC says. But it comes along with a new flu strain – subclade K, a variation of the influenza A(H3N2) virus – responsible for flu outbreaks in Japan, the U.K. and Canada. Health officials have been concerned the current flu vaccine may be a mismatch to the new variant, but are confident it has protection against serious illness.

Health officials aren't yet sure if the new flu strain is leading to more infections or more severe cases, "but what is clear is that cases are increasing, and we're seeing a lot of influenza cases increasing across the country, and that's a trend that we sure will continue into the new year," said Andrew Pekosz, who is the co-director of the Johns Hopkins Center of Excellence in influenza research and response, in a Dec. 16 video health briefing.

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Fewer Americans getting flu shots this season

Also potentially contributing to an increase in flu: a decline in Americans getting flu shots. While more than 47.6 million flu vaccinations have been given at retail pharmacies and physician medical offices so far in the 2025-2026 season, that's down about 3 million flu shots from last year, according to the CDC.

The government shutdown, which ran from Oct. 1 to Nov. 12, also likely meant a decrease in flu activity data, which could have affected vaccination rates, said Jennifer Nuzzo, professor of epidemiology and director of the Pandemic Center at Brown University School of Public Health, in a flu report published Dec. 19 by the Journal of the American Medical Association.

“We’re potentially heading into a flu season that could be quite a doozy, and we know we’re starting it with fewer data and, more crucially, fewer vaccinations,” she said.

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Flu has led to 1,900 deaths so far, three children, CDC says

CDC estimates that there have been at least 4,600,000 illnesses, 49,000 hospitalizations, and 1,900 deaths from flu so far this season. During the week ending Dec. 13, there were two pediatric deaths reported to the CDC, bringing flu-related pediatric deaths so far this season to three, the agency said.

In Colorado, where the CDC said flu-like activity was "very high," emergency department visits with a flu diagnosis increased 7% for the week ending Dec. 20, according to the Colorado Department of Public Health and Environment.

Influenza accounted for 7% of emergency department visits in Louisiana, up from about 6% the previous week, according to the Louisiana Department of Health. All respiratory illnesses including flu, COVID-19 and RSV made up nearly 9% of emergency visits, the department said.

In New York City, visits to hospital emergency rooms with a flu diagnosis increased to 8.75% for the week ending Dec. 20, up from 6.76% the previous week, according to the New York City Department of Health and Mental Hygiene.

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These states have high or very high flu activity

The CDC's FluView Interactive Map is based on outpatient visits to healthcare providers for influenza-like illness within a state or territory. These states and territories had high or very high levels:

• Colorado (Very High)

• Connecticut (High)

• District of Columbia (High)

• Idaho (High)

• Massachusetts (High)

• New Hampshire (High)

• New Jersey (High)

• New Mexico (High)

• New York (Very High)

• New York City (Very High)

• Puerto Rico (High)

• Louisiana (Very High)

• Georgia (High)

• Maryland (High)

• Michigan (High)

• North Carolina (High)

• South Carolina (High)

What are the latest flu symptoms?

Symptoms associated with H3N2 are similar to those of other influenza viruses and include:

• Fever

• Cough

• Runny nose

• Fatigue

• Muscle aches and chills

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How to protect yourself from the flu

It's not too late to get a flu vaccination. The CDC, World Health Organization and other leading medical institutions consider it the most effective way to prevent serious illness from the flu. Everyone 6 months and older is eligible for the flu vaccine unless they have a specified medical condition, such as an allergy to its ingredients or a previous severe reaction to the shot.

To help stop the spread of influenza, wash your hands often with soap and water for at least 20 seconds – or use an alcohol-based hand sanitizer, notes the New York State health department. Other tips to prevent the spread of the flu:

• Avoid touching your eyes, nose and mouth with unwashed hands.

• Stay home if you are sick.

• Avoid close contact with people who are sick.

• Cover your cough or sneeze with a tissue, then throw the tissue in the trash.

• Clean and disinfect frequently touched objects and surfaces.

Contributing: Mary Walrath-Holdridge

Mike Snider is a national trending news reporter for USA TODAY. You can follow him on Threads, Bluesky, X and email him at  mikegsnider  &  @mikegsnider.bsky.social  &  @mikesnider & [email protected].

This article originally appeared on USA TODAY: Flu cases on rise across US. New York hits weekly case record