A large new study published in The Lancet journal EClinicalMedicine has detected significant cognitive deficits in recovered COVID-19 patients. The research found the more severe the case, the greater the persistent cognitive problems, with hospitalized patients put on ventilators showing a decline equivalent to seven IQ points.
Early in 2020, before the pandemic kicked off, Imperial College London researcher Adam Hampshire was working with the BBC on a big, UK-wide cognitive survey. Called the Great British Intelligence Test, the project was designed to get a broad overview of the nation’s intelligence.
As the year progressed Hampshire realized the ongoing project afforded him a unique opportunity to investigate how this new disease affected cognition. By May the researchers had incorporated questions regarding COVID-19 into the survey.
As of December 2020 the researchers had collected data from 81,337 subjects. Around 12,000 subjects surveyed reported contracting COVID-19.
After adjusting for a variety of factors the researchers detected a significant relationship between COVID-19 and cognitive deficits. The severity of cognitive problems was directly related to the severity of the acute infection, with the greatest deficits detected in subjects admitted to hospital and put on a ventilator.
Key results of on the association between Covid-19 illness and cognitive abilities in hospitalised & non hospitalised members of the UK general public. 1/7 The severity of respiratory symptoms predicted cognitive performance months post recovery. https://t.co/DMU93E9zBA pic.twitter.com/uXjLLuSc7Q
— Adam Hampshire (@HampshireHub) July 23, 2021
“The scale of the observed deficit was not insubstantial,” the researchers write in the newly published study. “The 0.47 SD [standard deviation] global composite score reduction for the hospitalized with ventilator sub-group was greater than the average 10-year decline in global performance between the ages of 20 to 70 within this dataset. It was larger than the mean deficit of 480 people who indicated they had previously suffered a stroke (-0.24SDs) and the 998 who reported learning disabilities (-0.38SDs). For comparison, in a classic intelligence test, 0.47 SDs equates to a 7-point difference in IQ.”
The greatest cognitive deficits detected in the study were seen in tasks evaluating reasoning, planning and selective attention. The researchers note these findings fit with other long COVID studies citing problems with persistent “brain fog” and difficulties concentrating.
“There is a worrying association between COVID-19 illness and a broad range of higher cognitive function in the early chronic phase,” Hampshire notes on Twitter. “More research is needed to determine how long these deficits last and their biological/physiological basis.”
Mechanisms to explain the cognitive deficits are hypothesized in the study, including the possibility hypoxia is causing neurological damage. But the researchers are cautious to note there is still much to learn about the neurological effects of SARS-CoV-2 infection.
Derek Hill, a researcher from University College London (UCL), called the study “intriguing but inconclusive” when it was first published late last year on preprint servers. He noted several issues with the study, including the self-reported nature of the COVID-19 cases and the lack of data documenting how long these symptoms may be lasting post-infection. He particularly pointed out the cross-sectional nature of the study as prone to error.
“It does not look at whether COVID makes your cognition worse – it instead looks at whether people who have recovered from possible COVID do worse on the cognitive test than a control group,” Hill explained. “This type of methodology is more subject to error than a longitudinal study that looks at the same people before and after an illness.”
What is vital for researchers to unpack over the coming months and years is whether these post-COVID cognitive deficits are specifically due to SARS-CoV-2 infection, or whether they are related to the known cognitive dysfunctions that follow any kind of critical illness or viral infection. Respiratory diseases in particular have been linked with long-term cognitive impairments, but the new study does note, "the scale of deficits in cases who were not put on a ventilator, particularly those who remained at home, was unexpected."
A study published in Nature journal Neuropsychopharmacology earlier this year found 81 percent of hospitalized COVID-19 patients reported some kind of persistent cognitive impairment following discharge. Again, it is unclear how long these impairments may last or what the underlying mechanism is, but UCL clinical researcher Christina Pagel suggests the growing evidence is worrisome if we are to broadly let the disease spread through a community.
“I worry that once again we are watching an unfolding disaster while waiting for unequivocal evidence,” Pagel says on Twitter. “Unequivocal evidence on long term impacts will, by definition, take months or years. Maybe it never will – but so far, trajectory is towards more certain evidence not less. What if by the time there can be no doubt of long term problems in many people who’ve had cover, we’ve allowed millions more infections leaving hundreds of thousands more people affected.”
Speaking to PsyPost, Hampshire is cautious not to overstate his new findings. He stresses the need for urgent research on the topic and reminds people that the best course of action currently is to get vaccinated.
“We need to be careful as it looks like the virus could be affecting our cognition,” says Hampshire. “We do not fully understand how, why, or for how long, but we urgently need to find out. In the meantime, don’t take unnecessary risks and do get vaccinated.”
The new study was published in the journal EClinicalMedicine.
