COVID will likely reach levels in December not yet seen this year, combining with surges of flu, RSV, and other pathogens for a winter not so different from last year’s “tripledemic,” experts say.

Raj Rajnarayanan, assistant dean of research and associate professor at the New York Institute of Technology campus in Jonesboro, Ark., told Fortune that the U.S. is a “sitting duck” in the face of a “syndemic” winter.

It’s a term he prefers to “tripledemic,” as it acknowledges the impact of more than three pathogens on the healthcare system, and the need for policies to address the phenomenon, in addition to medical interventions.

“Strained hospital capacities, workforce exhaustion, burnout, a lack of effective therapeutic tools, poor communication, a lack of compliance [with COVID precautions], a lack of continuity planning, and the pervasive influence of social determinants of health” only make the nation’s delicate health infrastructure more fragile, he said.