Two new studies are offering clues on who might get long COVID. The first, published Tuesday in Cell, followed 209 COVID patients for up to three months after their initial diagnosis. Roughly a third of them reported having at least three long COVID symptoms (fatigue, brain fog, altered sense of smell, etc.) two or three months after being infected—and of that group, 95% had at least one of four biological factors the researchers pinpointed as potentially increasing one's chances of long COVID. They are: having a high viral load early on; the presence of specific autoantibodies, which end up attacking tissues; the reactivation of Epstein-Barr virus, which most adults are infected with; and having Type 2 diabetes.
Caveats abound, from the brevity of the study to the fact that 71% of patients had been hospitalized, making it tougher to say those factors play the same role in cases of mild infections. But as lead researcher Jim Heath tells the New York Times, "I think this research stresses the importance of doing measurements early in the disease course to figure out how to treat patients, even if we don’t really know how we’re going to use all that information yet." NBC News reports on another study, published Tuesday in the journal Nature Communications, that followed more than 500 COVID patients for a year. It found that those who developed long COVID had lower levels of specific antibodies in their blood shortly after becoming infected.
Specifically, the patients that developed long COVID tended to have lowered levels of the immunoglobulins IgM and IgG3—antibodies the immune system pumps out to help fight infection. When the antibody levels were aligned with other factors (middle age and a history of asthma among them), researchers were able to predict long COVID with 75% accuracy. One caveat here: Many of the patients studied were infected prior to the availability of vaccines, so it's unclear whether the risk factors would still hold among the vaccinated. (Read more long COVID stories.)