Immunological associations in post-infective fatigue syndromes including Long COVID-a systematic review and meta-analysis.

Abstract

The pathophysiology of post-infective fatigue syndromes (PIFS), including Long COVID, is unknown. This systematic review and meta-analysis aimed to investigate if PIFS is associated with persistent immune activation. PubMed, EMBASE, and Web of Science were searched for terms related to infection, fatigue, persistent symptoms, and immunological markers. adults and adolescents; Exposure: documented acute infection; Comparator: those who developed PIFS vs. recovered controls from the same exposure; and Outcomes: immunological biomarkers. Studies which documented acute infection, applied diagnostic criteria for PIFS, and assayed circulating immunologic markers were eligible. From 14,985 studies screened, 30 articles were included (n = 5102 participants; 833 PIFS/PIFS-like cases, n = 4269 recovered control participants) with many studies excluded by inadequate quality in eligibility criteria. The meta-analysis (11 studies; n = 413 PIFS cases, analysed with random-effects models) showed PIFS cases had increased: white cell counts at 3-6 months (Cohen's d: 0.41, 95% CI 0.09-0.74); and circulating levels of RANTES and TNFα at 6-12 months (Cohen's d: 0.45 [95% CI 0.16-0.73] and 0.30 [95% CI 0.04-0.57], respectively) compared to controls recovered from the same exposure. These findings provide cautious support for persistent immune activation in PIFS, but warrant further replication. Future studies should include better documentation of acute infection and PIFS case characterisation. ARL is supported by a National Health and Medical Research Council Practitioner Fellowship (Grant 1041897). CXS is supported by a Cancer Institute New South Wales Early Career Fellowship (2021/ECF1310). BZK is supported by the National Institute of Allergy and Infectious Diseases (AI 105781). RAE is supported by the National Institute for Health and Care.