New research published in The Lancet Psychiatry has offered the most comprehensive look at the long-term neurological effects of COVID-19 published to date, tracking more than one million people for up to two years. The findings revealed an increased risk of mood disorders such as depression and anxiety, following SARS-CoV-2 infection, returns to normal after a few months but increased rates of dementia are still being detected in older adults up to 24 months after the acute disease.
A year ago a team of researchers from the University of Oxford published a study indicating long COVID symptoms can still be detectable up to 12 months after an initial SARS-CoV-2 infection. Now, that same team has offered an even larger follow-up of COVID patients up to two years after their initial infection.
The study looked at 1.28 million COVID patients, and matched them to a control group of patients with any other kind of viral respiratory infection. The key goal was understanding what effects COVID-19 had specifically on the risk of 14 neurological and psychiatric conditions, compared to other viral infections.
The good news is that any increased risk of mood disorders after COVID, such as anxiety or depression, seemed to return to baseline within a couple of months after the acute illness. In children particularly the researchers found no difference at all in rates of depression or anxiety from COVID compared to other respiratory infections.
But in adults there were some signs of lingering neurological problems up to two years after COVID. Adults aged under 65 displayed higher rates of brain fog after COVID compared to other respiratory infections (640 cases per 10,000 people compared to 550 cases per 10,000 people).
Adults aged over 65 seemed to display the most significant long-term neurological problems, with increased rates of brain fog (1,540 cases per 10,000 compared to 1,230 cases), dementia (450 cases vs. 330), and psychotic disorders (85 cases vs. 60).
“… 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,” said lead on the new study, Paul Harrison. “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. It also appears that omicron, although less severe in the acute illness, is followed by comparable rates of these diagnoses."
Concerns over the effects of SARS-CoV-2 on neurodegenerative disease have been floated since the pandemic kicked off in 2020. In the years following the Spanish Flu pandemic in 1918, doctors saw sharp increases in rates of Parkinson’s disease and researchers have suggested some viral infections may accelerate the progression of pre-existing neurodegenerative disease.
Research presented a couple of months ago indicated there may already be signs of increased rates of Alzheimer’s, Parkinson’s and stroke in older COVID survivors. Max Taquet, a co-author on the new study, said it is important to note the absolute increases in dementia risk from COVID are still relatively low.
“I think it’s very clear that this is not a tsunami of new dementia cases,” Taquet said in a press call reported by STATNews. “Equally, I think it’s hard to ignore it, given the severity of the consequences of dementia diagnoses. A 1.2% increase in the population in absolute terms and compared to in other previous infections is hard to ignore.”
The strength of this study is in its robust control group allowing for a greater insight into the novel risk caused by SARS-CoV-2, as opposed to any general increased risk from other kinds of respiratory infection. In this case the study does suggest COVID may increase one's risk of dementia but exactly how that could be happening is still unclear.
Some researchers have begun to home in on how this novel coronavirus could be influencing neurological disease, such as in a recent study finding similarities between Alzheimer’s and long COVID. But plenty more work will be needed to really understand what the long-term effects of COVID are.
University College London researchers Jonathan Rogers and Glyn Lewis, who did not work on this new study, noted the new findings were concerning but also stressed how complex and heterogenous dementia is, so it is a little early to come to any conclusions as to the link between COVID and dementia.
“… dementia has an insidious onset and the cohort is likely to have had some participants with undiagnosed or subclinical cases at baseline,” write Rogers and Glyn in a commentary on the new research. “Although concerning, the findings regarding psychosis and dementia need replication in a cohort in which there is more thorough ascertainment of case status.”
The new study was published in The Lancet Psychiatry.
Source: University of Oxford