Covid-19 is associated with a higher risk of brain disease up to two years later

The risk of being diagnosed with a neurological or psychiatric condition up to two years after contracting covid-19 may be higher than with other respiratory infections, such as seasonal flu

from Jason Arun Murugesu

People who have had Covid-19 have a higher risk of being diagnosed with a neurological or mental illness up to two years later than those who have experienced other respiratory infections, such as seasonal flu.

Paul Harrison at the University of Oxford and colleagues analyzed the medical records of more than 1.25 million people worldwide who were diagnosed with covid-19 between January 20, 2020 and April 13, 2022.

The researchers compared the participants with people who experienced other respiratory infections during that time. In this control group, the researchers included only people who did not test positive for the coronavirus at any point in the time frame.

For both groups of participants, the team analyzed the risk of developing 14 neurological and psychiatric conditions in the two years after infection for three age groups: children under 18, adults aged 18 to 64, and adults over 65.

Previous studies have looked at neurological and psychological symptoms experienced by people in the six months following covid-19, but this is the first large-scale study to look for these effects up to two years after infection, according to the researchers.

“This is very important because for patients, clinicians and public health authorities … you want to know at what point after covid-19 you can be reassured that you are no longer at increased risk of receiving a psychiatric diagnosis,” says Harrison.

Among adults aged 18 to 64, the risk of being diagnosed with depression or anxiety for the first time in the two months after contracting the coronavirus was 75% and 60% higher, respectively, than for other respiratory infections. For depression, this increased risk fell to the same levels seen after exposure to other respiratory diseases on average 43 days after exposure, while for anxiety it was 58 days. Over two years, 18.2% of those infected with the coronavirus and 18.8% of those infected with other respiratory diseases were diagnosed with depression. Over the same period, 11.6 percent of those who recovered from COVID-19 and 11.5 percent of those infected with other respiratory illnesses were diagnosed with anxiety disorders.

However, the analysis found that the risk of being diagnosed with brain fog and epilepsy in adults aged 18 to 64 remained higher in people who had Covid-19 up to two years after infection, compared to those who had other respiratory infections.

In this age group, 6.4% were diagnosed with brain fog within two years of COVID-19, compared to 5.5% of participants who had other respiratory infections. Statistical analysis shows that this is a significant difference.

The risk of dementia was increased in those aged over 65 up to two years after Covid-19, with 4.5% diagnosed with dementia in the two years after Covid-19, compared with 3.3% in the control group.

Children were not found to have a higher risk of developing anxiety or depression after covid-19 than those who experienced other respiratory infections. However, they faced a higher risk of epilepsy or seizures up to two years after infection compared to those who had other respiratory infections, although the actual likelihood of developing these conditions remained small. Only 2.6 percent of children infected with the coronavirus developed epilepsy or seizures within two years of contracting the coronavirus.

This age group also had a three-fold increase in psychosis in the two years after covid-19 compared to those who experienced other respiratory infections – although only 1.8% of children were diagnosed with the condition in the two years.

The researchers also compared people in the US who caught different variants of the coronavirus. Rates of most neurological and psychiatric diagnoses are similar following infection with the delta or omicron variants, although the latter is generally associated with milder disease.

Why covid-19 increases the risk of various neurological or mental conditions is unclear, but there are possible explanations, Harrison says. The virus may persist in certain cells in the nervous system, or the immune system’s efforts against the coronavirus may result in some collateral damage to the brain, he says.

Aravinthan Varatharaj from the University of Southampton in the UK says these findings may reflect the fact that people at higher risk of neurological disease may be more likely to get covid-19 in the first place, but it may also reflect the impact of the coronavirus on the brain.

“Infections such as covid can affect the brain through a number of mechanisms, including signaling through the vagus nerve, activation of the immune system and changes in the blood-brain barrier,” he says.

Journal reference: The Lancet Psychiatry , DOI: 10.1016/S2215-0366(22)00260-7

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