Variant watch: Even mild cases may leave a mark on brain

A case of mild Covid-19 can lead to significant effects on the brain, according to a new study by a team led by scientists from Stanford and Yale universities, who found previously undiscovered biological mechanisms and markers that demonstrate how a Sars-CoV-2 infection leaves many with effects similar to chemotherapy.

The finding holds implications for rehabilitation of people with even mild cases and those suffering from so-called long Covid symptoms, which are still not properly understood. These effects have often manifested as what has loosely been known as brain fog, in which cognitive ability and memory functions are impaired.

The latest study, shared as a journal pre-print for peer review, now finds more signs of why this may be happening by studying how the virus, engineered to cause only mild disease, affected mice brains and the infection markers seen in people with and without such symptoms.

First, the researchers found signs of neuro inflammation by detecting specific markers for immune cells known as cytokines in spinal fluid up to seven weeks after an infection. These were found in the mice as well as 48 people who reported neurological long Covid symptoms, but the same markers were not present in 15 people who did not have these long-lasting symptoms.

The scientists then studied the brains of the mice and found “microglial reactivity” in a particular part of the brain. Microglia are a type of immune cells in the central nervous system.

These cells also limit the process of generation of new neurons in the hippocampus, the part of the brain that supports healthy memory function. Indeed, for the third part of the study, they found that there was a “stark decrease in new neuron generation” in the infected mice. They also found that another process of a healthy brain in which the myelin – it modulates the speed of neural impulses – is optimally maintained was impacted.

The authors add that they are yet to assess whether newer variants such as Omicron have a similar biological effect on the brain. But their study provides new biological insight that cognitive losses affect not only people who were hospitalised due to Covid-19 but also those that had mild disease.

“There are stark parallels between the cellular dysregulation that can happen after chemotherapy and even mild Covid-19. Understanding the neurobiological underpinnings of Long Covid will lay the groundwork for therapeutic strategies to address this neurological health crisis,” said Michelle Monje, neuroscientist at Stanford University and one of the authors of the study, in a tweet.

A second study, also shared this week, offers some hope. Researchers in Israel found that people who were fully vaccinated were significantly less likely to suffer from long Covid symptoms.After adjusting... those who received two doses were less likely than unvaccinated individuals to report (fatigue) by 64%, (headache) by 54%, (weakness) by 57%, and (persistent muscle pain) by 68%, said the researchers from Safed, Israel.