Millions of people who have had Covid-19 still face a higher risk of neurological and psychiatric conditions, including brain fog, dementia and psychosis, two years after their illness, compared with those who have had other respiratory infections, according to the single largest study of its kind. They also face an increased risk of anxiety and depression, the research suggests, but this subsides within two months of having Covid-19. Over two years the risk is no more likely than after other respiratory infections. The findings are published in the Lancet Psychiatry journal. Almost 600m Covid-19 cases have been recorded worldwide since the start of the pandemic, and there has been growing evidence that people who survive the disease face increased risks of neurological and psychiatric conditions. Previous studies have found that people face higher risks of several neurological and mental health conditions in the first six months after infection. Until now, however, there has been no large-scale data examining the risks over a longer time period. The new study, by the University of Oxford and the National Institute for Health and Care Research Oxford Health Biomedical Research Centre, analysed 1.28m Covid-19 cases over two years. Dr Max Taquet, who led the analyses at the University of Oxford, said: “The findings shed new light on the longer-term mental and brain health consequences for people following Covid-19 infection. The results have implications for patients and health services and highlight the need for more research to understand why this happens after Covid-19, and what can be done to prevent these disorders from occurring, or treat them when they do.” The study analysed data on 14 neurological and psychiatric diagnoses from electronic health records mostly from the US. It found that in adults the risk of depression or anxiety increased after Covid-19 but returned to the same as with other respiratory infections within about two months. However, the risk of some other neurological and mental health conditions remained higher after Covid-19 than for other respiratory infections at the end of the two-year follow-up. Adults aged 64 and under who had Covid-19 had a higher risk of brain fog (640 cases per 10,000 people) compared with those who had other respiratory infections (550 cases per 10,000 people). In those aged 65 and over who had Covid-19, there was a higher occurrence of brain fog (1,540 cases per 10,000 people), dementia (450 cases per 10,000 people) and psychotic disorders (85 cases per 10,000 people) compared with those who previously had a different respiratory infection (1,230 cases per 10,000 for brain fog, 330 cases per 10,000 for dementia and 60 cases per 10,000 for psychotic disorder). Results in children showed similarities and differences to adults. The likelihood of most diagnoses after Covid-19 was lower than in adults, and they were not at greater risk of anxiety or depression than children who had other respiratory infections. However, like adults, children recovering from Covid-19 were more likely to be diagnosed with some conditions, including seizures and psychotic disorders. More neurological and psychiatric disorders were seen during the Delta variant wave than with the prior Alpha variant. The Omicron wave was linked with similar neurological and psychiatric risks as Delta. The researchers cautioned that there were some important limitations to consider. The study may underrepresent self-diagnosed and asymptomatic cases of Covid-19 as these are unlikely to be recorded. It also did not look at the severity or length of conditions after Covid-19 and how they compare with other respiratory infections. Prof Paul Harrison, who led the study at the University of Oxford, said: “It is good news that the excess of depression and anxiety diagnoses after Covid-19 is short-lived, and that it is not observed in children. However, it is worrying that some other disorders, such as dementia and seizures, continue to be more likely diagnosed after Covid-19, even two years later.”