The study, published in The Lancet Psychiatry on Wednesday, found that the risk of disorders like cognitive deficit (also known as ‘brain fog’), psychotic disorders, and epilepsy was elevated even two years after a COVID diagnosis. 

Researchers analyzed data from almost 1.5 million COVID patients sourced from TriNetX, which compiles health records from 89 million patients across eight countries. Researchers compared COVID patients to an equal number of patients diagnosed with a non-COVID respiratory infection, who acted as a control group.

The study found that COVID patients were 13 times more likely to be diagnosed with any one of 14 tracked neurological conditions six months after catching the disease, compared to patients of other respiratory diseases. In particular, COVID patients were 36 times more likely to be diagnosed with cognitive deficit and 33 times more likely to be diagnosed with dementia six months after catching COVID.

Researchers also tracked when the chance of developing one of thes e conditions would return to the same level as non-COVID patients. For conditions like cognitive deficit, dementia, epilepsy, insomnia, and psychotic disorder, the risk never returned to the baseline level by the end of the studied time period.

The study also uncovered an increased risk of mood and anxiety disorders in the weeks following a diagnosis of COVID-19. That risk returned to baseline levels within a few months, and both COVID and non-COVID patients reported equal incidences of these conditions within 15 months.

Child COVID patients also had an increased chance of developing conditions like brain fog, insomnia, and other disorders following a COVID-19 diagnosis. The risk of ‘brain fog’ returned to a baseline level after about two months, but the chance of developing other conditions like epilepsy remained elevated after two years. Children were not found to have an increased risk of mood or anxiety disorders compared to non-COVID patients.

New variants, like the more transmissible but less deadly Omicron variant, did not seem to change the risk of developing one of these conditions. The study found that despite lower death rates, new variants showed “similar” risks of “neurological and psychiatric outcomes” as earlier strains. 

The study only analyzed patients whose COVID diagnosis was entered into their medical record, and so may not reflect those who never sought professional medical care for COVID, such as those who were asymptomatic or had mild symptoms. The research also did not examine how vaccination altered the chance of developing a neurological condition, but referred to earlier work by some of the authors that found that vaccination reduced the risk of psychotic disorders, while leaving the risk of anxiety and depression unchanged.

Not just the brain

Scientists are still investigating just how broadly COVID affects the body. Catching the disease has been tied to chronic fatigue, muscle weakness, hair loss, erectile dysfunction, stroke, and cardiovascular illness. 

Last week, a study from the Yale School of Medicine and the Icahn School of Medicine at Mount Sinai found lower rates of cortisol, a stress hormone, in those with long COVID. Low levels of cortisol have been tied to muscle weakness and fatigue. 

An earlier study from Oxford University found that the brains of COVID patients would shrink by an amount equal to a decade’s worth of aging, particularly in areas that governed taste and smell. At the time, researchers cautioned against connecting that decline to a higher risk of developing a condition like ‘brain fog.’

The U.S. Centers for Disease Control and Prevention found in late May that one in five adult Americans who survived COVID were suffering from some form of long COVID. Experts estimate that up to 4 million Americans might not be working due to chronic conditions after catching COVID.