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 .
