Look for flu and COVID-19 infections to ramp up in the coming weeks, U.S. health officials say, with increases fueled by holiday gatherings, too many unvaccinated people and a new version of the coronavirus that may be spreading more easily.

High levels of flu-like illnesses were reported last week in 17 states — up from 14 the week before, the Centers for Disease Control and Prevention said Friday.

“Folks are traveling a lot more this season. They want to see their families,” said the CDC’s Dr. Manisha Patel. “And all of that sort of adds to the mix” in the spread of viruses.

Health officials are keeping an eye on a version of the ever-evolving coronavirus, known as JN.1. The omicron variant was first detected in the U.S. in September and now accounts for an estimated 20% of cases. The CDC expects it to reach 50% in the next two weeks, Patel said.