Even a mild case of Covid-19 can cause long-term brain damage

Researchers at Oxford University in England reported that several months after study participants had Covid-19, they had more brain-tissue loss and more brain-size shrinkage than participants who did not have the disease. They used brain scans from the United Kingdom’s Biobank—a research resource with data from half a million volunteers—that were collected from 2014 through early March 2020, and they invited hundreds of original volunteers aged 51 to 81 for a second round of scans between February and March 2021.

With nearly 800 volunteers, the new study is the largest set of Covid-19 brain-imaging analyses to date. It’s also the first to focus on patients with mostly non-severe illness and to include pre-infection data from the same people. The study is published in the peer-reviewed journal Nature.

The brain scans and cognitive scores of participants who had Covid-19 showed greater changes between the two time periods than those of the participants who did not have Covid. On average, the participants who had Covid suffered from greater tissue damage and brain shrinkage, and has less ability to do complex tasks.

The study had too few cases of influenza to draw comparisons, but brain differences among 11 volunteers who developed non–Covid-19 pneumonia between imaging sessions did not substantially overlap with brain regions implicated in the Covid-19 analysis. This could indicate that the study’s findings are specific to infection by the novel coronavirus, not respiratory infection in general.

It is unclear how long the cognitive effects of Covid-19 might last. A recent report in JAMA Neurology suggests the changes in some patients might endure, particularly for those with more severe disease. However, in a written FAQ provided to news media, the study’s lead author, Gwenaëlle Douaud, suggested that the damage observed in her team’s study might improve in due course: “Since the abnormal changes we see in the brain of the infected participants might be related to their loss of smell, it is possible that recovering their smell might lead to these brain abnormalities becoming less marked over time. Similarly, it is likely that the harmful effects of the virus (whether direct, or indirect via inflammation or immune reaction) decrease over time after infection.”

How best to manage patients’ cognitive symptoms remains an area of robust study, according to Dr. S. Andrew Josephson. The current analysis, he said, “also emphasizes just how important it is to continue to work to understand the mechanisms of these neurological symptoms and whether vaccination or severity of illness modifies them.”