December 14, 2022 12:01 AM EST

Long COVID—a condition with symptoms ranging from respiratory to neurological, from crushing fatigue to chronic pain—can be debilitating. And in some cases, according to a new report from the National Center for Health Statistics (NCHS), Long COVID may even be fatal.

From January 2020 through June 2022, Long COVID contributed to more than 3,500 deaths in the U.S., according to death-certificate data analyzed by NCHS researchers. About 0.3% of death certificates that listed COVID-19 as an underlying or contributing cause of death also mentioned Long COVID, for an age-adjusted death rate of 6.3 per 1 million people.

“The good news is that…by and large, post-COVID is not a fatal condition,” says Dr. Aaron Friedberg, an internal-medicine physician who treats Long COVID patients at the Ohio State University Wexner Medical Center (and who was not involved in the new research). “Most people do get better with post-COVID.”

But Dr. Ziyad Al-Aly, an assistant professor at the Washington University School of Medicine in St. Louis and a Long COVID researcher (who also wasn’t part of the NCHS report), fears the problem may be worse than it looks on paper.

Read More: Long COVID Isn’t the Only Post-Viral Illness

In the report, researchers looked at death certificates that mentioned COVID-19 as a contributing or underlying cause of death, then zoomed in on those that explicitly mentioned Long COVID or a related term, such as “post-COVID” or “long-haul COVID.” That process overlooks anyone who had but didn’t test positive for COVID-19 or was never properly diagnosed with Long COVID, Al-Aly says. The number of death certificates that mention Long COVID has increased with time, which suggests that awareness of the condition was lower earlier in the pandemic, he adds.

Plus, some post-COVID complications are less visible than common symptoms such as fatigue and brain fog. Studies suggest COVID-19 survivors are at increased risk of serious health issues including organ failure, heart attack, and blood clots—but those things may not be attributed to the virus on a death certificate, Al-Aly says.

“Our data systems are built on this archaic assumption that…if you have a viral infection, most of the action happens in the first 30 days,” Al-Aly says. In reality, though, many viruses can trigger long-lasting health consequences, whether they’re linked to the initial infection or not.

Chronic illnesses, including Long COVID, can also exacerbate pre-existing conditions, potentially pushing a patient from stable to critical, Friedberg notes. According to the NCHS’ report, heart disease was the underlying cause of almost 9% of deaths related to Long COVID, while cancer, Alzheimer’s, respiratory disease, and diabetes each accounted for between 2% and 3%. There have also been documented cases of people with Long COVID dying by suicide.

Almost 80% of the deaths involving Long COVID were among adults ages 65 and older, according to the NCHS report, and a similar percentage were among white adults. Though Long COVID seems to be more prevalent among women than men, just under half of related deaths were recorded among women.

Regardless of the exact numbers in the report, Friedberg says its findings underscore a familiar message: do whatever you can to avoid getting COVID-19, which is the best way to reduce the risk for Long COVID. Vaccines, masks, and ventilation are important tools, both for your current and future health.

“We don’t really have any way to stop post-COVID right now. It’s a lottery every time you get COVID,” Friedberg says. “I’d love to be able to cancel that lottery.”

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Write to Jamie Ducharme at jamie.ducharme@time.com.

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