Prolonged inflammation in patients hospitalized for coronavirus disease 2019 (COVID-19) resolves 2 years after infection

Blood Biomarkers of Long COVID: A Systematic Review

BACKGROUND

Long coronavirus disease (COVID; LC) affects millions of people worldwide. The exact mechanisms which result in a broad, undulating and detrimental symptom profile remain unknown. Blood biomarkers associated with LC have been described; however, consensus on these remains elusive, in part due to a lack of continuity between studies on a universally accepted definition of LC. This systematic review aimed to consolidate current knowledge of blood biomarkers associated with the prevalence of LC on the basis of the World Health Organisation (WHO) clinical definition of this condition.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Observational, cross-sectional, and randomised control studies published in the English language that studied blood biomarkers associated with the WHO definition of LC. All studies included participants who were ≥ 18 years old and group sizes ≥ 10 participants, and were compared against a control group without any known co-morbidities.

METHODS

A systematic literature search was conducted according to Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines and prospectively registered on Prospero (ID: CRD42022373121). The Cochrane, Embase, PubMed and Web of Science databases were searched from inception to January 2024. Search results were gathered using Rayyan software and data extracted using Microsoft Excel. The reporting recommendations for tumour markers prognostic studies (REMARK) questionnaire was used to assess the quality of the included studies.

RESULTS

A total of 45 observational and one interventional study comprising 4415 participants were included in this review which identified 525 blood biomarkers thought to be associated with LC. Three blood biomarker subtypes were associated with the development of LC: (1) immunological and inflammatory dysfunction, (2) endothelial/vascular dysfunction and (3) metabolic and clotting abnormalities.

DISCUSSION AND CONCLUSIONS

Our data are consistent with previous findings; however, no single biomarker was sufficiently associated with LC prevalence and instead a profile of biomarkers across various physiological systems may be more clinically useful. In all, 196 studies were excluded due to a lack of an adequately healthy comparator group and/or failure to meet the WHO LC definition. This demonstrates a need for further research incorporating a universal LC definition across all disease severity groups and symptom profiles, and longitudinal data reflecting the relapsing and remitting nature of this condition. Further investigation into blood biomarkers of LC, including clear reporting of healthy comparator groups and the investigation of acute and chronic biomarker changes, within the context of medical practice, may support the development of curative/restorative approaches.

Sex-specific biphasic alpha-synuclein response and alterations of interneurons in a COVID-19 hamster model

BACKGROUND

Coronavirus disease 2019 (COVID-19) frequently leads to neurological complications after recovery from acute infection, with higher prevalence in women. However, mechanisms by which SARS-CoV-2 disrupts brain function remain unclear and treatment strategies are lacking. We previously demonstrated neuroinflammation in the olfactory bulb of intranasally infected hamsters, followed by alpha-synuclein and tau accumulation in cortex, thus mirroring pathogenesis of neurodegenerative diseases such as Parkinson's or Alzheimer's disease.

METHODS

To uncover the sex-specific spatiotemporal profiles of neuroinflammation and neuronal dysfunction following intranasal SARS-CoV-2 infection, we quantified microglia cell density, alpha-synuclein immunoreactivity and inhibitory interneurons in cortical regions, limbic system and basal ganglia at acute and late post-recovery time points.

FINDINGS

Unexpectedly, microglia cell density and alpha-synuclein immunoreactivity decreased at 6 days post-infection, then rebounded to overt accumulation at 21 days post-infection. This biphasic response was most pronounced in amygdala and striatum, regions affected early in Parkinson's disease. Several brain regions showed altered densities of parvalbumin and calretinin interneurons which are involved in cognition and motor control. Of note, females appeared more affected.

INTERPRETATION

Our results demonstrate that SARS-CoV-2 profoundly disrupts brain homeostasis without neuroinvasion, via neuroinflammatory and protein regulation mechanisms that persist beyond viral clearance. The regional patterns and sex differences are in line with neurological deficits observed after SARS-CoV-2 infection.

FUNDING

Federal Ministry of Health, Germany (BMG; ZMV I 1-2520COR501 to G.G.), Federal Ministry of Education and Research, Germany (BMBF; 03COV06B to G.G.), Ministry of Science and Culture of Lower Saxony in Germany (14-76403-184, to G.G. and F.R.).

Two-Year Longitudinal Study Reveals That Long COVID Symptoms Peak and Quality of Life Nadirs at 6-12 Months Postinfection

Background

Few longitudinal studies available characterize long COVID outcomes out to 24 months, especially in people with nonsevere acute coronavirus disease 2019 (COVID-19). This study sought to prospectively characterize incidence and duration of long COVID symptoms and their association with quality of life (QoL) from 1-24 months after mild-to-moderate COVID-19 using validated tools in a diverse cohort of unvaccinated people infected with SARS-CoV-2 in 2020.

Methods

At 1-3, 6, 12, 18, and 24 months post-COVID-19, 70 participants had orthostatic vital signs measured, provided blood, and completed surveys characterizing symptoms, QoL, and return to pre-COVID-19 health and activities using validated tools (FLU-PRO+, Fatigue Severity Scale, Insomnia Severity Index, General Practitioner Assessment of Cognition, Patient Health Questionnaire Depression 8-Item, Generalized Anxiety Disorder 7-Item, 36-Item Short-Form Health Survey, EuroQol EQ-5D-5L).

Results

During the study period, 33% of participants experienced long COVID (had not returned to pre-COVID-19 health status and reported at least 1 symptom >90 days postinfection); 8% had not returned to their pre-COVID-19 health status 24 months postinfection. Long COVID symptoms peaked 6 months post-COVID-19, frequently causing activity limitations. Having long COVID was significantly associated with decreased QoL in multiple domains. Frequencies of orthostatic hypotension and tachycardia reflected levels reported in the general population. Within-person weight increased significantly between months 1 and 6. Long COVID was associated with pre-COVID-19 obesity and hyperlipidemia, but not with high-sensitivity C-reactive protein levels 1-3 months postinfection.

Conclusions

Long COVID occurs in a significant proportion of unvaccinated people, even if the acute illness was not severe. Long COVID prevalence peaked 6-12 months post-COVID-19, and a small proportion of participants still reported not returning to their pre-COVID-19 health status 24 months post-COVID-19.