The more times you catch COVID, the sicker you’re likely to get with each reinfection. That’s the worrying conclusion of a new study drawing on data from the U.S. Veterans Administration.

Scientists stressed they need more data before they can say for sure whether, and why, COVID might get worse the second, third, or fourth time around. But with more and more people getting reinfected as the pandemic lurches toward its fourth year, the study hints at some of the possible long-term risks.

To get a handle on the health impact of reinfection, re-reinfection and even re-re-reinfection, three researchers—Ziyad Al-Aly from the Washington University School of Medicine plus Benjamin Bowe and Yan Xie, both from the V.A. St. Louis Health Care System—scrutinized the health records of 5.7 million American veterans.

Some 260,000 had caught COVID just once, and 40,000 had been reinfected at least one more time. The control group included 5.4 million people who never got COVID at all. Al-Aly, Bowe and Xie tracked health outcomes over a six-month period and came to a startling conclusion. “We show that, compared to people with first infection, reinfection contributes additional risks,” they wrote in their study, which hasn’t been peer-reviewed yet but is under consideration for publication in Nature.

Every time you catch COVID, your chance of getting really sick with something—likely COVID-related—seems to go up, Al-Aly, Bowe and Xie found. The risk of cardiovascular disorders, problems with blood-clotting, diabetes, fatigue, gastrointestinal and kidney disorders, mental health problems, musculoskeletal disorders and neurologic damage all increase with reinfection—this despite the antibodies that should result from repeat infections.

All of the conditions are directly associated with COVID or have been shown to get worse with COVID. “The constellation of findings show that reinfection adds non-trivial risks,” the researchers warned.

This risk could become a bigger deal as more people get reinfected. Globally, the death rate from COVID is going down, thanks in large part to growing population-wide immunity from past infection and vaccines.