A highly infectious norovirus variant is currently making its way through the US and UK.

The variant, identified as GII.17, caused a noticeable increase in cases last year across both the US and Europe after it first appeared in April. Presently, this stomach bug is once again gaining traction in the US and the UK. In the UK, where both the historically dominant GII.4 and GII.17 are active, the latter accounts for nearly 19% of infections.

Experts emphasize the variant’s exceptional contagiousness, with the Centers for Disease Control and Prevention highlighting its role in causing approximately 50% more cases than other strains in the US, as reported by the Daily Mail.

While the prevalence of GII.17 has diminished in the UK, it still ranks as the second most common variant, making up 19% of cases as of December 7, according to the UK Health Security Agency. Meanwhile, the previously dominant GII.4 has reasserted itself as the leading strain, responsible for 31% of cases for the 2025/2026 season up to early December.

This virus is colloquially termed the ‘rib-cracking’ winter virus because those afflicted often experience such severe vomiting that it can lead to rib discomfort, according to HealthAndMe.

Dr. Scott Roberts, an infectious disease specialist at Yale University, explained to TODAY that new strains can spread quickly, as evidenced by last year’s events.

“So far, we’re not yet to the level that we were at last year, which was really our worst year since pre-Covid… but it’s certainly going up. Time will tell how bad it will get. Now is the time to be vigilant. I expect things to get worse before they get better.”

Norovirus, also known as the ‘winter vomiting bug’ is spread by close contact with an infected person or touching surfaces that have the virus on them and then touching your mouth. It can also be passed on by eating food that has been prepared by someone with norovirus.

If you get symptoms, the NHS recommends staying away from work or school for two days after the sickness and diarrhoea have passed.

It also highlights that fruit juice or fizzy drinks can exacerbate the sickness, and you should instead drink fluids such as water or squash.