With many gathering for the holidays, local doctors are warning about a new strain of the flu, possibly making this season look even worse than last year.

A Northwestern doctor said it's still too soon to tell if the flu shot protects against this new strain called subclade K. However, they said if you got the vaccine and you do get sick, you likely won't have a severe case.

This year's flu is fast-moving, with a lot more cases expected after the holidays.

As people make their way through the Daley Plaza Christkindlmarket on its final week, doctors warn that large crowds could be what spreads the flu this holiday season, whether you are traveling or inside with friends and family.

"This flu is just different than the strain that we saw last year. It's similar, but we are seeing that it is moving faster," said Dr. Santina Wheat with Northwestern Medicine.

Dr. Wheat said Chicago emergency rooms and urgent cares are busy with the Respiratory Syncytial Virus, norovirus, and the dominant subclade K flu strain.

"If you start to have symptoms, absolutely stay home so you are not spreading this to them," she said.

Dr. Wheat said even mild versions of the virus could severely hurt someone with underlying health conditions.

So far this season, there have been 4.6 million reported flu cases, and nearly 2,000 people have died from the flu in the U.S., including three kids.

"We think this subclade K virus is evading population immunity, meaning more people are susceptible to infection," said Professor Andrew Pekosz, Johns Hopkins Bloomberg School of Public Health.

Doctors said the symptoms come on rapidly and include a 103 to 104 degree fever, body aches, cough, fatigue, and vomiting, mostly in kids. 

While the virus is peaking in some places, like in New York, Dr. Wheat said Chicago is not seeing those numbers yet.

"We are still considered to have a low amount of flu activity," she said.

She reminds the public that it's a good idea to wash hands with soap and water, hydrate, and mask up, especially if you are traveling to a place where flu cases are peaking. She adds there's a small benefit to this super flu compared to last season's.

"The people that I see with the flu, they are recovering faster than I saw some of them recover last year," she said.

Dr. Wheat also said that while RSV and flu cases are going up, COVID-19 cases are trending downward. She said if you do feel sick, test yourself for flu or COVID in case you need antiviral medications.