As H3N2 flu brings US to its knees, experts warn Canadians, urge them to exercise caution; here’s what you need to know as holiday season ends

The H3N2 flu strain is landing more people in the hospital in the United States, and experts are urging Canadians to exercise caution amid a “perfect environment” for spread and a fresh round of case numbers expected in this country next week. The development comes as the flu strain lands more Americans in hospital.

H3N2 is a subtype of the influenza virus. A virus that commonly causes seasonal flu outbreaks. According to the US The Centers for Disease Control and Prevention (CDC) reported that around 7.5 million Americans have been infected and 81,000 have landed in the hospital this flu season, Global News reported.

“Some parts of the United States are reporting the highest rates of flu hospitalizations since they’ve kept records,” Dr. Fahad Razak, an internal medicine physician at St. Michael’s Hospital and professor at the University of Toronto, was quoted as saying by Global News.


The CDC revealed that in the week ending December 20, 2025, one in four (25.6 percent) cases of every influenza test conducted in America returned positive.

For the week ending December 20, 2025, 19,053 people were rushed to hospital in the US with the flu. Five children died in the U.S. in the week ending Dec. 20 after an association with influenza, the CDC further stated.

This was a sharp rise as compared to the week ending December 13, 2025. Around 15.7 percent of tests came back positive in the week ending Dec. 13 and nine percent for the week ending December 6, 2025. The strain that is currently the dominant strain in the US and Canada is a strain called H3N2 subclade K.

Subclade K

According to USA Today, subclade K is a mutation of influenza A H3N2. It was previously called A(H3N2) virus subclade J.2.4.1. Influenza A is the virus linked with the term "flu" and has evolved into many different strains over time.

Canadians should be cautious, says Dr. Fahad Razak

The holiday season is coming to an end, and according to Dr. Razak, now is the time that Canadians must exercise caution in the coming weeks. “We have data that is very suggestive that we’re having an incredibly bad flu season here in Canada as well,” he said, as quoted by Global News.

“We can look to other countries; the experience in parts of Europe, now the United States, and before that in Australia and Japan suggested some of the worst, or the worst, flu seasons on record,” he added. Razak said the “enormous amount of human flow between the two countries, especially over the holidays,” should give Canadians pause.

“That is a perfect environment for an infectious disease to spread,” he said as Canadians and Americans return from seeing family on both sides of the border over the holiday season. “If you think about our border with the United States, it’s the kind of border where when you have a high rate of illness that’s transmissible on one side, it’s nearly impossible to keep it out from the other side,” he added.

Hospitalization from influenza rises in Canada

Health Canada’s latest data suggests that the rate of hospitalization from influenza in the country has nearly doubled compared to the previous week of available data, with infections now up almost 30 percent, according to Global News.

Canada saw 11,646 new cases of flu being detected for the week ending December 13, 2025, which means 27.7 percent of all the tests conducted in the country came out positive.