That holiday feast that brought you joy and connected you with family and friends could gift you something less delightful in the new year.

Public health officials are warning that the so-called “tripledemic” of COVID-19, flu and respiratory syncytial virus could get worse in January, courtesy of holiday gatherings and New Year’s Eve parties.

“These are highly contagious viruses — and people have generally put COVID-19 and COVID vaccination behind them,” Dr. William Schaffner, an infectious disease professor at Vanderbilt University Medical Center and medical director of the National Foundation for Infectious Diseases, told CNN this week. “They haven’t been all that attentive to flu. They’re not wearing masks. And if you’re close together with other people, it’s an opportunity for all three of these viruses — flu, COVID and even RSV — to spread from one person to another. So, we do expect a post-holiday surge in these viruses.”

And that’s not counting respiratory misery from the common cold, either. All of those ills surged after Thanksgiving, public health experts warned. And more will likely follow the December holidays.

Even the sheer volume of people who have been stuck at airports together as thousands of flights have been canceled in the past week could increase the risk.

The Centers for Disease Control and Prevention estimates that, as of Dec. 23, more than 18 million people in the United States had been sickened by influenza, with 190,000 cases resulting in hospitalization and 12,000 deaths so far during this flu season.

Monday, Lori Tremmel Freeman, chief executive officer of the National Association of County and City Health Officials, told CNN by email that COVID-19 cases and deaths are likely to increase post-holiday, “likely attributable to increased travel across the country, large family gatherings, fewer people being up to date on their COVID-19 vaccinations and flu shots, and fewer people following mitigation measures, such as masking and social distancing,” the news organization reported.

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Even before the holidays, the Dallas Morning News reported via MedicalXpress that “unseasonably-early waves of the flu and respiratory syncytial virus, are hitting cities across the U.S. and filling pediatric hospitals with sick children. While most older children and adults with healthy immune systems can fight such an infection with little issue, the viruses can still cause nasty symptoms like cough, congestion, fever and body aches.”

Health experts note that the measures that became common to protect against COVID-19 — masking, frequent handwashing and maintaining some physical distance — are good tools against other respiratory viruses, as well.

In a CDC media briefing early in December, Dr. Rochelle Walensky, the organization’s director, urged Americans to get vaccinated. “First and foremost: Get vaccinated. For two of the three viruses discussed today, there are vaccines,” she said, referring to flu and COVID-19.

As for RSV, vaccines are in the works, per a Mayo Clinic podcast. “A number of vaccine manufacturers have developed vaccines, including a couple of them through phase three trials,”  Dr. Gregory Poland, head of Mayo Clinic’s Vaccine Research Group, said. ”Very likely, certainly before this time next year, I think we’ll have a licensed RSV vaccine for adults, and then they’ll move clinical trials down to kids. So we’re definitely making progress there.”

At the briefing, Dr. Sandra Fryhofer, board chair at the American Medical Association and an internal medicine physician in Atlanta, warned the public to take precautions. She said that flu was “almost nonexistent” during the first two years of the COVID-19 pandemic, as people wore masks, washed their hands and stayed isolated. “And so I think there was a there’s probably like a sense of complacency. We think we’ve forgotten how bad flu can be. But this year’s season is a shout out that it can get really bad and it’s here, so people need to get vaccinated.”

The symptoms of flu, RSV and COVID-19 can be nearly indistinguishable without testing.