A new international study published in the Journal of Medical Virology reveals a possible explanation for the symptoms that continue to affect thousands of people even after the acute phase of COVID-19. The research detected, in the blood of these individuals, microclots associated with chronic inflammation, which could account for extreme fatigue, muscle pain, breathing difficulties and other prolonged effects of the infection.
The research, published in the Journal of Medical Virology, analysed plasma samples from 50 patients with persistent COVID-19 symptoms and 38 healthy people from South Africa and France. Using advanced imaging cytometry and fluorescence microscopy techniques, the scientists identified significantly higher quantities of microclots and inflammation markers in those who reported complaints weeks or months after recovering from the infection.
These microclots — small clusters of amyloid proteins resistant to natural degradation — were found in greater numbers and larger sizes in the samples from symptomatic patients. In addition, they were strongly associated with structures released by cells of the immune system, known as neutrophil extracellular traps (NETs), which aggravate inflammatory processes and can obstruct blood vessels.
The researchers also confirmed the presence of myeloperoxidase (MPO), neutrophil elastase (NE) and circulating DNA, three markers associated with immune activation and the formation of these traps. When these elements are found at high levels, they suggest a persistent inflammatory state in the body.
Using machine learning algorithms such as Random Forest, the team showed that combining the number of microclots with MPO levels makes it possible to distinguish, with high accuracy, individuals affected by post-COVID symptoms. The model achieved 91% accuracy and 86% sensitivity, which could pave the way for new diagnostic tests.
Despite these promising results, the authors caution that further studies are needed with patients with other inflammatory conditions — such as diabetes or lupus — to confirm the specificity of these markers in post-acute COVID-19.
According to the scientists, the persistence of these microclots in the blood, together with continuing inflammation, may be preventing a full recovery, mainly affecting circulation in the small blood vessels. This phenomenon can lead to oxygen deficits and a worsening of symptoms over time, even in the absence of the active virus.
The research, carried out in collaboration between Stellenbosch University (South Africa) and the INSERM institute (France), represents an advance in knowledge about the after-effects of COVID-19 and points to new ways of detecting and treating them.
Read more about the study at https://onlinelibrary.wiley.com/doi/10.1002/jmv.70613
