Covid-19 patients face an increased risk of dementia, brain fog and other neurological conditions up to two years after an infection, a major new study has shown.
Researchers from the University of Oxford reviewed the health records of more than 1.25 million patients and analysed data from 14 neurological and psychiatric diagnoses, alongside different types of Covid infections.
They found that, over a two-year period, the chance of being diagnosed with various neurological and psychiatric conditions is, in the worst cases, two to three times higher after Covid than for other respiratory infections.
The research, published in the Lancet Psychiatry, also showed that children face a two-fold increased risk of epilepsy and seizures: 260 in 10,000 under-18s develop the conditions after Covid, compared to 130 in 10,000 following another respiratory infection, according to the paper.
However, the likelihood of most neurological and psychiatric diagnoses after Covid-19 was lower in children than in adults, the researchers added.
Professor Paul Harrison, lead author of the study, said: “The results have important implications for patients and health services as it suggests new cases of neurological conditions linked to Covid-19 infection are likely to occur for a considerable time after the pandemic has subsided.
“Our work also highlights the need for more research to understand why this happens after Covid-19, and what can be done to prevent or treat these conditions.”
Dr Rachel Sumner, a senior research fellow at Cardiff Metropolitan University, who was not involved in the research, said the study shows “another layer of potential future harm for health services across the world.”
She added: “Long-term effects of Covid will cause longer-term economic harm in the form of extensive health service utilisation and employment absenteeism or even unemployment, which is a risk for some that are most affected by the conditions highlighted in the study.
“It is also of concern that patients that experience Covid and go on to develop some of these disorders will continue to have delays in diagnosis and treatment with healthcare systems that are struggling to deal with both Covid infections and backlogs of patient waiting lists.”
The study analysed data on 14 neurological and psychiatric diagnoses taken from the health records of 1,284,437 patients in the US who had a confirmed Covid infection on or after 20 January.
This included 185,748 children (under 18), 856,588 adults between 18 and 64 years old, and 242,101 adults over 65. These individuals were matched to an equal number of patients with another respiratory infection to act as a control group.
The study showed that adults aged 18-64 who had Covid-19 up to two years previously had a higher risk of brain fog and muscle disease, compared to those who had other respiratory infections over the same period. In adults aged 65 and over, there was a higher occurrence of brain fog, dementia and psychotic disorder.
Among the over-65s, there were 450 new diagnoses of dementia per 10,000 people s within two years of a Covid infection, compared to 330 cases for the control group.
Dr Max Taquet, who led the analyses for the research, said it was “very clear that this is not a tsunami of new dementia cases” but argued that it was too “hard to ignore” the paper’s findings “given the severity of the consequences of dementia diagnosis”.
He added: “We don't want to claim there's a tsunami, we also don't don't want to ignore that number altogether.”
Prof Harrison said the numbers for new neurological and psychiatric diagnoses after a Covid-19 infection were “not trivial” and “need to be set against the increasing burden of mental health problems … that may have occurred in the whole population because of the pandemic.”
Paul Garner, an emeritus professor in evidence synthesis in global health at the Liverpool School of Tropical Medicine, cautioned that “we need to be careful in the interpretation of the reported small increases in dementia and psychosis: these are, in my opinion, more likely to be related to the societal upheaval and dystopia we have been living through rather than being a direct effect of the virus.”
The study also found that, in adults, the risk of being diagnosed with depression or anxiety initially increased following Covid-19 but, after a relatively short time, returned to the same levels seen with those infected by a different respiratory pathogen. Children were also deemed not to be at greater risk of anxiety or depression after Covid.
The emergence of the Delta variant was meanwhile associated with significantly higher six-month risks of anxiety, insomnia, cognitive deficit, epilepsy or seizures, and ischaemic strokes, but a lower risk of dementia when compared to those diagnosed with Covid-19 with just before the Delta wave. Omicron leads to similar risks, the researchers added.
“Our findings shed new light on the longer-term mental and brain health consequences for people following Covid-19 infection,” said Dr Taquet.
“It is good news that the higher risk of depression and anxiety diagnoses after Covid-19 is relatively short-lived and there is no increase in the risk of these diagnoses in children.
“However, it is worrying that some other conditions, such as dementia and seizures, continue to be more frequently diagnosed after Covid-19, even two years later.”
Acknowledging the limitations of the study, the researchers said the results likely underrepresented people with mild or asymptomatic Covid. They added that the paper does not explain how Covid elevates the risk of developing a neurological and psychiatric condition.
