• Jessica Holland, Diarmuid Sheehan, Sinead Brown, Susan O'Flanagan, Stefano Savenelli, Fiadhnait O'Keeffe, and Jessica Bramham.
• University College Dublin. Electronic address: Jess.f.holland@gmail.com.
• Am. J. Med. 2024 Oct 1.

BackgroundAltered immune response and cognitive difficulties have been demonstrated in studies of post-COVID syndrome, including differences in immune status and cognitive functioning in the months following infection. This review aimed to examine immune status and cognitive differences in post-COVID Syndrome twelve or more weeks after COVID-19 infection. A further aim of this review was to explore a link between immune response and the cognitive deficits observed in this group.MethodsA systematic review was carried out of PubMed, PsychInfo, EMBASE and Web of Science electronic databases of observational studies 12+ weeks after COVID-19 infection, with assessment of immune status and cognitive function in post-COVID Syndrome samples. This review protocol was recorded on PROSPERO with registration number CRD42022366920.ResultsFollowing eligibility screening, eleven studies met inclusion criteria and were selected for our review. Six of eight studies which examined between group differences in specific domains suggested impaired cognition in the Post COVID Syndrome population, with the domains of executive function particularly affected. Of the eleven studies with immune data, nine studies reported increased markers of inflammation in the Post COVID Syndrome group, when compared to an age and gender matched "healthy control" sample, or population norms. Finally, when immune function and cognition are examined together, six studies presented results indicating a significant association between elevated immune response and cognitive function.ConclusionThis review highlights the frequency of cognitive difficulties months after COVID-19 infection and explores heighted immune response as a predictor of this change. Six studies suggest that immune status is a predictor of cognitive function, examining a marker of immune function and objective cognitive performance at 12 or more weeks following infection. Future studies of cognitive function in Post COVID Syndrome are needed to explore this relationship, and underlying mechanisms leading to changes in cognitive performance.Copyright © 2024. Published by Elsevier Inc.

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