A recent study led by the University of Bristol challenges the notion that long COVID is caused by an immune inflammatory response to COVID-19.
The research sheds new light on the condition that affects approximately two million individuals in the UK alone. While emerging data suggest that immune activation can persist for months after COVID-19, the study indicates that this may not be the underlying cause of long COVID.
The study aimed to investigate whether ongoing immune activation and inflammation could explain the development of long COVID.
Analyzing Immune Responses
The researchers collected and analyzed immune responses from blood samples of 63 patients who had been hospitalized with mild, moderate, or severe COVID-19 at the early stages of the pandemic, prior to the availability of vaccines.
The patients' immune responses were assessed at three months, eight months, and twelve months after hospital admission. Among these patients, 79% reported at least one persistent symptom, with breathlessness and excessive fatigue being the most common.
Dr. Laura Rivino, the lead author of the study and Senior Lecturer at Bristol's School of Cellular and Molecular Medicine, explained that the cause of long COVID is still not well understood, with theories suggesting an inflammatory immune response or reactivation of latent viruses as potential triggers.
However, the study's findings indicated that immune dysfunction and inflammation observed at three months in patients with severe symptoms tended to resolve over time.
By the twelve-month mark, the immune profiles and inflammatory levels of patients with severe disease resembled those of mild and moderate cases.
Interestingly, the analysis did not reveal a direct association between long COVID symptoms and immune-inflammatory responses in any of the patients, after accounting for age, sex, and disease severity.
While patients with severe COVID-19 exhibited a higher number of long COVID symptoms compared to mild and moderate cases, the study did not find evidence linking these symptoms to immune inflammatory responses.
Furthermore, there was no significant increase in immune cells targeting SARS-CoV-2 at three months. Instead, T-cells targeting the latent cytomegalovirus (CMV) showed a slight increase at low levels, suggesting that prolonged T-cell activation observed in severe cases might be "bystander driven," driven by cytokines rather than the SARS-CoV-2 virus itself.
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Need for Larger Studies
Dr. Rivino emphasized the need for larger studies involving a greater number of patients, including vaccinated and non-vaccinated individuals, to gain a deeper understanding of the relationship between inflammation, immune activation, and long COVID. Such studies could help identify potential therapeutic strategies for this debilitating condition.
The findings from this study provide valuable insights into the complex nature of long COVID and the potential factors contributing to its development.
Further research is warranted to unravel the underlying mechanisms and explore targeted interventions to alleviate the burden of long COVID on affected individuals.
The study was published in the journal eLife.
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