Even Mild Covid-19 Infections May Change the Brain, New Study Finds

Scans taken before and after a case of coronavirus reveal tissue damage and accelerated loss of gray matter

image of a male doctor holding a tablet with an mri scan on it
Researchers examined magnetic resonance imaging (MRI) scans of the brains of 785 British participants before and after Covid-19 infection. Solskin via Getty Images

Even mild cases of Covid-19 may cause damage in the brain, mostly in areas related to smell, according to a new study.

When scientists compared the loss of gray matter that naturally occurs in people who have not Covid-19 to those that had been previously infected with the virus, they found signs of accelerated brain aging, including a greater loss of gray matter. The research, which was published in the journal Nature, may be the largest study of its kind to date, reports CNN’s Nadia Kounang.

“It is brain damage, but it is possible that it is reversible,” lead author Gwenaëlle Douaud, an associate professor of neurosciences at the University of Oxford, tells Benjamin Ryan for NBC News. “But it is still relatively scary because it was in mildly infected people.”

To see if and how Covid-19 changes the brain of its host, the research team evaluated more than 400 people who had the virus between March 2020 and April 2021. The participants, who were between 51 to 81 years old, underwent brain scans years before their Covid-19 infection and again an average of four-and-a-half months after recovering from the virus. Most had mild symptoms; only 15 of the participants were hospitalized with the disease.

When scientists compared those MRI images with scans of 384 uninfected people of a similar age, they found shrinkage and tissue damage primarily in brain areas related to sense of smell. Older participants experienced brain-related declines more profoundly, per NBC News.

“To me, this is pretty convincing evidence that something changes in brains of this overall group of people with Covid,” says Serena Spudich, chief of neurological infections and global neurology at the Yale School of Medicine, who was not involved in the study, to Pam Belluck reports for the New York Times

As people age, their brains naturally lose a tiny amount of gray matter each year, which provides nutrients and energy to the brain. But those that had Covid-19 appeared to lose between 0.2 percent and 2 percent more gray matter over the three years between scans than those who didn’t get the virus. Despite the finding that Covid-19 may be changing individuals’ brains, researchers warn against panic. 

“To make a conclusion that this has some long-term clinical implications for the patients I think is a stretch,” Spudich says to the Times. “We don’t want to scare the public and have them think, ‘Oh, this is proof that everyone’s going to have brain damage and not be able to function.’”

The study also evaluated whether the virus impacted an individual’s brain function and found that those who had the greatest brain tissue loss also performed the worse on cognitive tests. While the work found some link between infection and brain function, it’s unclear why these deficits happen after a Covid-19 infection and how long they last.

“We don’t know that it actually means anything for the patient’s quality of life or function,” says Benedict Michael, an associate professor of neurological infections at the University of Liverpool, who was not involved in the study, to the Times.

Next, researchers plan to investigate if these changes persist over time or if the damage is reversible.