Get ready for a brutal winter: Experts warn about a medical issue that will be problematic this year

With the end of Daylight Saving Time on November 2 days are getting shorter, and colder. Winter is officially set to start in little over a month, (December 21 in the US) but we are already deep into flu season. As temperatures fall, we become more susceptible not just to colds but also to viruses like influenza.

Flu is currently doing the rounds in the United States, Europe and Japan although activity is reported to be low so far this year, and affecting mainly children and young adults.

A(H3N2) flu strain present in the United Kingdom

In the UK, influenza activity started earlier than usual and has been showing mixed trends. Flu-related acute respiratory infections (ARI) are rising but for the moment, hospital admissions remain stable. According to the national Health Security Agency, the majority of the cases witnessed have been infections from the A(H3N2) variant.

In Japan, flu cases have been surging with the average weekly number reported at medical institutions rising from from 6.29 to 14.90, way over the alert level of 10. And like the UK, flu season has arrived earlier in Japan, with the first reported incidents at the end of September.

With that scenario, what can we expect in the US? The latest report from the CDC paints a similar picture - activity is low nationally but is increasing. The most frequent strain is A(H3N2) which mutated up to seven times over the summer, increasing in severity. Those mutations also mean that the virus (renamed subclade K) is different to the strain included in this year’s vaccine.

The CDC informs in their latest report (Week 45, ending November 8, 2025) that 72 influenza viruses have been reported by public health laboratories - of which, 67 were influenza A and the remaining five were influenza B. Of the 53 influenza A viruses subtyped during Week 45, 15 (28.3%) were influenza A(H1N1)pdm09 and 38 (71.7%) were A(H3N2).

Flu activity remains low in the US for now

While activity is low, judging by the timing, many experts expect this year’s flu season to be high severity, and potentially even worse than last year’s which saw test positivity rates hit 31.6%, the highest figures in 15 years.

Dr. Daniel Kuritzkes, who is in charge of the infectious diseases department at Brigham and Women’s Hospital in Boston believes that the current situation in the UK and Japan is an indication of where things could be heading in the US. “We do generally see similar patterns in North America, as we see in Western Europe. So, it is likely that we’ll see a similar flu season here to what’s being experienced currently in the UK”.

The mutating A(H3N2) strain is a cause for concern says Dr. Jill Foster, professor at the University of Minnesota Medical School. “It has undergone a fairly significant number of mutations, so it is likely to cause a problem. The flu virus that is circulating does appear to be more pathogenic. It is more easily transmitted, and when transmitted, causes more severe disease”.

This year’s flu shot

There have been no influenza-related pediatric deaths in the US as of the time of publication (one has been reported in Alberta, Canada). The trivalent seasonal influenza vaccine for 2025-2026 is available, according to the FDA they contain:

Flu shots can be given to anyone over 6 months of age. It is available at over 50,000 locations nationwide including Costco Pharmacy, Safeway, Kroger, Meijer and other retail clinics. Contact your health care provider for more information.

In general, flu cases in the US don’t increase very much until December, then tend to peak in January or February, with a second peak in March.

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