Covid can cause brain disorders two years after infection, study shows

Covid-19 significantly increases the risk of developing dementia, psychosis and brain fog two years after infection, according to the first comprehensive study of the disease’s lingering neurological and psychiatric effects.

Long Covid, often defined as symptoms experienced for 12 weeks or more after a Covid diagnosis, includes a range of symptoms from fatigue and shortness of breath to problems related to the brain, such as a lack of mental clarity. Scientists estimate that it could affect more than 100 million people worldwide.

Researchers from the University of Oxford analyzed the electronic health records of 1.25 million people diagnosed with Covid and a matched control group consisting of an equal number of patients with other respiratory infections. The data, covering 14 brain disorders, was provided by the US-based TriNetX global health research network.

The impact of Covid was greatest among people 65 and older, 4.5 percent of whom developed dementia in the following two years, compared with 3.3 percent of the control group. For psychotic disorders, the figures were 0.85 percent in Covid patients and 0.6 percent in controls.

The most significantly increased risk in younger adults ages 18 to 64 was cognitive impairment, also known as brain fog. It affected 6.4 percent of people who had Covid in the past two years and 5.5 percent of controls.

“The results have important implications for patients and health services, as they suggest that new cases of neurological disorders linked to Covid infection are likely to occur well after the pandemic has subsided,” said Paul Harrison, senior author of the study published in The Lancet Psychiatry.

But he added, “We’re not talking about a tsunami of neurological and psychiatric diseases.”

Max Taquet, who led the analysis, said two findings stood out in the 185,000 patients under the age of 18. Children were twice as likely to develop epilepsy or seizures, he said — 2.6 percent developed the condition after Covid, compared to 1.3 percent after another respiratory infection.

Second, Taquet added: “Children have a threefold increased risk of psychotic disorder, although this is rare – 18 in 10,000 in the two years after Covid.”

But the research also found that the impact of Covid was sometimes short-lived. “Excessive risks of depression and anxiety after Covid disappear within two to three months, with no overall excess of cases over the two years,” Taquet said.

The researchers tried to distinguish between the effects of different Sars-Cov-2 variants, although there is inevitably less long-term data for strains that emerged more recently, especially Omicron.

“The emergence of the Delta variant was associated with an increased risk of several conditions,” Taquet says. “With Omicron as the dominant variant, although we see much milder symptoms immediately after infection, similar rates of neurological and psychiatric diagnoses are seen as with Delta,” he added.

Taquet said the findings suggested the burden on health care systems could continue, even with variants that are less severe in other respects.

Looking at lung Covid in a broader sense, the Oxford scientists emphasized that much research was still needed on all aspects of the condition, from definition and prevalence to biological causes and possible treatments.

“My feeling is we know a lot less than we think we know about long Covid,” Harrison said. “There are many more questions than answers,” Taquet agrees.

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