Doctors at Northwell Health say they've seen a big surge in cases of COVID, flu and RSV.

Together, the three illnesses are known as the "tripledemic."

"We ran about 11,000 tests last week so we're very busy," says senior vice president of Lab Services at Northwell Health Dwayne Breining. "What's concerning for us is the cases of flu are rising at like 30% per week. The hospitalizations are rising at 75% per week."

Hospitalizations of RSV and COVID are also becoming a big concern. "We're not yet seeing a lot of RSV in our pediatric population, which is great news and I think part of that is because there are new products on the market for babies and for pregnant women to get vaccinated," says senior vice president of Pediatric Services at Northwell Health Annemarie Stroustrup.

Doctors say there are multiple reasons why cases and hospitalizations are rising.

"There aren't as many people getting vaccinated. The other thing is the virus continues to mutate," says Breining.

Doctors say the vaccines can prevent hospitalizations. Doctors say with the holidays coming up next week, you shouldn't go to a large gathering if you're not feeling well.