In October, a group of researchers, mostly from Stanford University, published a non-peer-reviewed study finding that COVID-19 may infect fat cells directly, a novel discovery that suggests overweight and obese people may be at increased risk for severe disease and long COVID.

“[Our study’s] data suggest that infection of fat tissue and its associated inflammatory response may be one of the reasons why obese individuals do so poorly when infected with SARS-CoV-2,” Dr. Catherine Blish, a professor at Stanford University Medical Center and a lead author on the study, told Reuters.

Blish and her team studied the adipose cells—or fat cells—of patients who died of COVID-19. The researchers found that COVID-19 not only infected the cells but also inflamed them, a response associated with severe COVID-19 cases. The findings suggest that the more overweight someone is the more susceptible that person may be to severe COVID infections. Someone carrying extra weight likely has more excess fat tissue that could be infected.

COVID-19’s ability to invade fat cells may have long-term implications for overweight or obese people infected with the virus.

“If adipose cells constitute a reservoir for viral infection, obesity may contribute not only to severe acute disease, but also to long-COVID syndrome,” the researchers note in the study.

Michael Toole, an epidemiologist at the Burnet Institute in Melbourne, said in an interview that by serving as a reservoir, the fat cells may be effectively “hiding” COVID-19 and spreading it to other areas in the body, increasing the risk that patients suffer from long-COVID symptoms months after they recovered from their initial infections.

Toole says that if the study passes peer review, it could have implications on treatment options since existing COVID-19 treatments do not generally target body fat.

“This paper is another wake-up call for the medical profession and public health to look more deeply into the issues of overweight and obese individuals, and the treatments and vaccines we’re giving them,” Barry Popkin, a professor of nutrition at the University of North Carolina at Chapel Hill, tells the New York Times.

In the U.S., 42.4% of people are obese and 73.6% of people are overweight, but only select states prioritized obese groups in their initial vaccine rollouts.

Toole says the study provides more evidence that overweight and obese people need to be considered in how the world prevents, treats, and manages COVID-19.

“I would definitely include the morbidly obese in the most [at risk] groups, says Toole. “We’ve known that obesity is the No. 1 risk factor for severe disease for some time, followed by diabetes and some other chronic disease, but obesity stands out.”