By now, it’s abundantly clear that COVID-19 is not always an illness that clears quickly and leaves no trace. Millions of people in the U.S., and even more around the world, have Long COVID, the name for symptoms that last months or even years after an infection.
Now, a new report from the U.S. Centers for Disease Control and Prevention (CDC) helps quantify just how often COVID-19 is linked to subsequent health issues. Among U.S. adults younger than 65 who have had COVID-19, roughly one in five has developed a health condition that may be related to the virus, the report says. Among people 65 or older, about one in four has.
To reach those findings, CDC researchers used electronic health records to track more than 350,000 U.S. adults who had confirmed COVID-19 cases. They tracked these people for up to a year after their diagnoses to see if they developed at least one of 26 conditions linked to post-COVID-19 illness—including heart disease, respiratory problems, asthma, kidney disease, neurologic conditions, diabetes, and mental health conditions. For comparison, they also tracked a group of 1.6 million U.S. adults who had not had COVID-19, but sought medical care for other reasons during the study period.
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From that comparison, it was clear that COVID-19 survivors were at increased risk of developing almost all of the 26 conditions. The most dramatic risk differences between COVID-19 survivors and the general population were in developing respiratory symptoms and pulmonary embolisms, a type of blood clot that can lead to shortness of breath and chest pain. People who’d had COVID-19 were about twice as likely to develop both conditions.
There were some limitations to the data. The researchers used one specific electronic health record network, so the patient base may not be perfectly representative of the U.S. population. It’s also possible that doctors were looking more closely for the analyzed conditions in COVID-19 survivors than in those who hadn’t had the virus, or that some people had undiagnosed conditions before they got infected. (People with a documented, recent history of one of the 26 conditions were excluded from the study.) The researchers also didn’t account for a person’s COVID-19 vaccination status, and data collection ran only through November 2021, so it’s impossible to say how newer COVID-19 variants like Omicron fit into the picture.
Still, the study provides even more evidence that COVID-19 can cause problems that last much longer than an acute infection does. Even if symptoms like coughing, fever, and fatigue clear up in a matter of days, the virus can leave a lasting mark in ways that aren’t immediately apparent.
That’s cause for serious concern, particularly given how contagious the currently circulating variants are. Almost 60% of the U.S. population had been infected as of February, according to CDC estimates, and that number is almost certainly much higher now. “As the cumulative number of persons ever having been infected with SARS-CoV-2 increases, the number of survivors suffering post-COVID conditions is also likely to increase,” the authors of the new report write.
These conditions can be serious or even debilitating—some with Long COVID have had to leave their jobs or drastically change their lifestyles—and it’s not always possible to predict who will be affected. The best way to avoid post-COVID complications, experts often say, is to avoid catching the virus in the first place, and to be vaccinated and boosted if you do.
Write to Jamie Ducharme at jamie.ducharme@time.com.
