Cognitive impairment following SARS-CoV-2 infection: study adds to existing evidence, but finds important exceptions

After many types of infection, cognitive impairment has been reported. This is also true in the case of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It is, however, unclear whether deficiencies following SARS-CoV-2 infection improve over time.

To address this gap in research, a new eClinicalMedicine study evaluated the presence, magnitude, persistence, and correlations of effects in community-based cases.

Background

Research has demonstrated continued cognitive impairment after SARS-CoV-2 infection. These deficits have been seen to increase with the severity of illness during the acute phase. Cognitive impairments have also been reported in individuals with long-term symptoms following COVID-19, referred to most commonly as long COVID.

The UK Office for National Statistical (ONS) estimated in January 2023 that out of the 2 million individuals in the UK with self-reported long COVID, 52% and 39% were experiencing difficulty concentrating and memory loss or confusion, respectively. Ongoing symptoms are associated with lower mental health, reduced ability to work, and wellbeing. Further, the cognitive decline caused by SARS-CoV-2 could get accelerated with age.

Previous studies mostly examined small, hospitalized cohorts, considered individuals infected in the first year of the pandemic, used dichotomized classifications, and generally had shorter follow-ups.

No studies have conducted a holistic analysis to examine the effects of both SARS-CoV-2 infection and symptom duration. Furthermore, few have longitudinally analyzed the cognitive trajectories of individuals to infer whether recovery relates to cognitive performance.

About this study

This study used a validated cognitive assessment tool to address a few questions of interest. The tool had retrospective reflective survey data from a large UK voluntary cohort and self-report symptom assessment. The questions of interest were: (1) Is there any association between COVID-19 and cognitive performance? (2) Do ongoing symptoms and symptom duration influence the association between COVID-19 and cognitive performance? (3) Do the associations between COVID-19 and cognitive performance change over time?

The recruited participants comprised individuals with and without SARS-CoV-2 infection and varying symptom duration. Effects of COVID-19 on reaction time and cognitive accuracy scored were estimated using multivariable linear regression models. The weights used were inverse of the probability of participation, and confounders were also adjusted for. A longitudinal analysis evaluated change in cognitive performance between rounds.

Key findings

Individuals with community-based SARS-CoV-2 infection showed cognitive deficits but only in the groups with ≥12 weeks symptom duration, relative to non-infected individuals. A longitudinal analysis of these individuals showed that deficits persisted for almost two years since infection.

In the first round of testing, lower cognitive task accuracy scores were seen among participants with positive SARS-CoV-2 infection status. The deficits were comparable in scale to the effect of presentation to the hospital during illness, exhibiting moderate or mild symptoms of psychological distress, or an increase in age of approximately ten years. No evidence was found on the adverse effect of SARS-CoV-2 infection on average reaction time during tasks.

Importantly, among participants who reported feeling recovered and “back to normal,” no detectable impairment was observed. The prevalence of symptoms of psychological distress is partly mediated by observed cognitive deficits. This suggested that the reduction of psychological distress, fatigue, and functional impairment is only partially associated with recovery.

Conclusions

A key limitation of the study was the unavailability of certain data that would have been very informative, such as cognitive assessment data before SARS-CoV-2 infection, information on prior neurovascular and neurodegenerative comorbidities, and so on. Also, the array of cognitive tasks used here was not exhaustive.

The results are also limited in terms of their generalizability because the cohort was not representative of the general population. Finally, the study relied on voluntary prospective logging of symptoms via a smartphone app, which could lead to data being imperfect and incomplete.

In sum, deficits in cognitive accuracy were observed in individuals with more than 12 weeks of symptoms following SARS-CoV-2 infection in the first year of the pandemic. Participants with ongoing symptoms at initial testing did not show a marked recovery at a 9-month follow-up. The scale of deficits observed could significantly alter the quality of life and daily functioning at an individual level as well as socioeconomic impacts on society.

In the future, more efforts are needed to identify individuals affected by ongoing symptoms following SARS-CoV-2 infection. This is because the ongoing element of long COVID appears to be a superior predictor of cognitive impairment rather than symptom duration. Future research should also investigate the mechanisms and trajectories of recovery from ongoing symptoms following COVID-19.

Written by

Dr. Priyom Bose

Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of Madras, India. She is an active researcher and an experienced science writer. Priyom has also co-authored several original research articles that have been published in reputed peer-reviewed journals. She is also an avid reader and an amateur photographer.