This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.
Brain fog (difficulty remembering, concentrating and thinking) has been linked with COVID-19.
Researchers analysed the cognitive performance of more than 140,000 people. They included people whose symptoms of COVID-19 had not resolved, those who had resolved symptoms (including symptoms that had been persistent), and others who had not had COVID-19. They found that memory and thinking were most impacted by COVID-19 in people who:
- were infected by early strains of the virus
- had unresolved symptoms for more than 12 weeks
- had been admitted to intensive care.
The findings contribute to understanding of the impact of COVID-19 on memory and thinking.
More information about COVID-19 can be found on the NHS website.
The issue: what factors influence the impact of COVID-19 on memory and thinking
COVID-19 has been linked with brain fog. But data on the long-term impact of COVID-19 on memory and thinking is largely lacking. Researchers sought to identify factors associated with cognitive deficits lasting up to a year or more.
What’s new?
This study, in 2022, included more than 140,000 people who had taken part in previous work (REACT study, which investigated how many people had been infected with COVID-19, when and where). Participants completed a cognitive assessment to measure aspects of cognitive performance such as memory and planning. The researchers compared the performance of people whose symptoms of COVID-19 had not resolved, those who had resolved symptoms (including symptoms that had been persistent), and those who had not had COVID-19.
They found that cognitive impairments could last more than a year after COVID-19. People who had COVID-19 for short periods of time (less than 12 weeks), and those who had persistent symptoms that eventually resolved, had slight cognitive deficits unlikely to be evident to them in everyday life (equivalent to 3 IQ points).
Memory, reasoning, and planning were the aspects of cognitive function most affected by COVID-19.
Compared with those who had not had COVID-19, people were more likely to have moderate cognitive impairment if they:
- were infected with the original strain of the virus (almost twice as likely)
- had ongoing symptoms (more than twice as likely)
- had been admitted to intensive care (almost 4 times more likely).
Why is this important?
The researchers found that on average, COVID-19 was associated with slight deficits in cognitive performance that are unlikely to affect everyday life. These deficits were greater for people who were infected earlier in the pandemic, had unresolved persistent symptoms or, in particular, had been admitted to intensive care.
The researchers say it is reassuring that later strains of the virus had a smaller association with cognitive function. It was promising for people with long COVID that those whose persistent symptoms had finally resolved performed at similar levels to those whose illness was short-term or who had asymptomatic infections.
People who reported cognitive symptoms were slightly more likely to complete the assessment than those who did not report symptoms, meaning the data could overestimate the proportion of people with cognitive deficits.
The researchers did not know participants’ cognitive scores before COVID-19, which means it is not possible to conclude that the scores had changed because of the infection, although they undertook thorough analyses to account for potentially confounding factors.
What’s next?
These findings strengthen the evidence for the long-term impact of COVID-19 on cognition. The researchers call for more research into the different ways that COVID-19 has affected people over the longer term and the mechanisms that underpin those effects. People left with cognitive difficulties following COVID-19 need greater support and understanding, they say.
What do these results mean for my practice?
You may be interested to read
This is a summary of: Hampshire A, and others. Cognition and memory after COVID-19 in a large community sample. New England Journal of Medicine 2024; 390: 806 – 818.
Information about the larger project this study is part of can be found on the Imperial College website.
Read more NIHR Evidence on long Covid
Funding: This study was funded by the NIHR Long COVID Programme and UK Research and Innovation.
Conflicts of Interest: No relevant conflicts were declared. Full disclosures are available on the original paper.
Disclaimer: Summaries on NIHR Evidence are not a substitute for professional medical advice. They provide information about research which is funded or supported by the NIHR. Please note that the views expressed are those of the author(s) and reviewer(s) at the time of publication. They do not necessarily reflect the views of the NHS, the NIHR or the Department of Health and Social Care.
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