Two years after having Covid-19, diagnoses of brain fog, dementia and epilepsy are more common than after other respiratory infections, a study by the University of Oxford suggests.
But anxiety and depression are no more likely in adults or children two years on, the research found.
More research is needed to understand how and why Covid could lead to other conditions.
Experts say the virus disrupted daily life as well as making people ill.
Previous research has suggested that adults are at an increased risk of brain and mental health conditions in the six months after a Covid infection.
This study looked at the risks of 14 different disorders in 1.25 million patients two years on from Covid, mostly in the US. It then compared them with a closely-matched group of 1.25 million people who had a different respiratory infection.
In the group who had Covid, after two years, there were more new cases of:
- dementia, stroke and brain fog in adults aged over 65
- brain fog in adults aged 18-64
- epilepsy and psychotic disorders in children, although the overall risks were small
For example, children’s risk of developing epilepsy after Covid was 260 in 10,000, compared to 130 in 10,000 after another respiratory infection.
Their risk of developing a psychotic disorder also increased after Covid – to 18 in 10,000 – but it is still a rare condition.
Some disorders became less common two years after Covid, including:
- anxiety and depression in children and adults
- psychotic disorders in adults
The increased risk of depression and anxiety in adults lasts less than two months before returning to normal levels, the research found.
Prof Paul Harrison, lead study author, from University of Oxford’s psychiatry department, said it was “worrying” that some disorders, such as dementia and seizures, are more likely to be diagnosed after Covid-19, even two years later.
But he said it was “good news” that depression and anxiety cases after Covid were “short-lived”, and not seen in children.
The researchers said the numbers affected were “hard to ignore” but were “not a tsunami”, and some would be likely to need medical attention which could add to the pressure on health services.
The study, published in the Lancet Psychiatry, did not track individual people over two years – instead it analyzed the number of people with a new diagnosis two years after their infection.
It also did not look at how severe each condition was after diagnosis or how long they lasted, and whether these are similar after Covid compared with other infections.
They stopped short of calling these conditions “long Covid”, although brain fog – or problems with memory and concentration – is a typical symptom.
Last winter’s Omicron variant was less likely to cause long Covid symptoms than previous variants, recent research suggests.
Although less severe than the Delta variant, Omicron appears to lead to similar risks of brain and mental health conditions, this study found.
The study has some limitations – it did not look at how Covid could cause brain and mental health disorders, although some experts say it could be explained by the development of micro-clots in the blood.
Dr Jonathan Rogers and Prof Glyn Lewis, from University College London, who were not involved in the research, said the study highlighted “some clinical features that particularly merit further investigation”, but they added that more studies were needed to confirm the findings.
Prof David Menon, from the University of Cambridge, said the impact of being in hospital with Covid was “equal to 20 years of ageing (between 50 and 70)”.
Paul Garner, emeritus professor in evidence synthesis in global health at Liverpool School of Tropical Medicine, said the Covid pandemic had changed people’s lives in many different ways.
He said the small increases in dementia and psychosis were “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.”