Norovirus rates have skyrocketed by 340% this season. Here’s where the ‘winter vomiting disease’ is spreading and why

The CDC reported 91 norovirus outbreaks the week of Dec. 5, 2024, up from 69 the week before. By comparison, up to 41 outbreaks were reported during that same week the previous three seasons. (Credit: Tom Merton—Getty Images)

Plenty of people likely kicked off 2025 hunched over a toilet—but not because they’d imbibed too much on New Year’s Eve. Norovirus, informally dubbed the “winter vomiting disease,” is making its rounds this winter.

Weekly test positivity rates have so far surged by 340% during the 2024–25 season, according to a Fortune analysis of Centers for Disease Control and Prevention (CDC) data recorded as three-week moving averages. Norovirus test positivity reached a season high of 22% the week ended Dec. 21, up from 5% the week ended Aug. 3. Just since the week ended Nov. 16, the rate had jumped from 11%, a 109% increase in five weeks.