By Pat Anson, PNN Editor

An immune system response to the COVID-19 virus has been suspected as a possible cause of Long Covid, a poorly understood disorder that causes chronic fatigue, brain fog, insomnia, chest pain and other symptoms long after the initial infection.  

But a small new study in the UK suggests that Long Covid may not be an inflammatory immune reaction to the SARS-CoV-2 virus. Instead, the body appears to be responding to the activation of dormant viruses many of us already have in our systems.

"Long Covid occurs in one out of 10 COVID-19 cases, but we still don't understand what causes it,” said Laura Rivino, PhD, Senior Lecturer at the University of Bristol's School of Cellular and Molecular Medicine. “Several theories proposed include whether it might be triggered by an inflammatory immune response towards the virus that is still persisting in our body, sending our immune system into overdrive or the reactivation of latent viruses such as human cytomegalovirus (CMV) and Epstein Barr virus (EBV)."

Rivino and her colleagues collected and analyzed blood samples from 63 Covid patients with mild, moderate or severe symptoms who were hospitalized at the start of the pandemic -- before vaccines were available – and tested them again 3, 8 and 12 months after their admission.  

Their findings, published in the journal eLife, show that patients with severe symptoms had significant dysfunction in their T-cell profiles after three months. T-cells are white blood cells released by the immune system to fight bacteria and viruses.

Further analysis showed there was no rapid increase in immune cells targeting SARS-CoV-2, but there was an increase in T-cells targeting CMV -- a common virus that is usually harmless but can stay in the body for life once you’re infected with it. That suggests that the prolonged T-cell activation observed at three months in severe patients may not be driven by SARS-CoV-2, but instead may be "bystander driven" by dormant viruses that were reactivated.  

"Our findings suggest that prolonged immune activation and long COVID may correlate independently with severe COVID-19. Larger studies should be conducted looking at both a larger number of patients, including if possible vaccinated and non-vaccinated COVID-19 patients,” said Rivino. "Understanding whether inflammation and immune activation associate with long COVID would allow us to understand whether targeting these factors may be a useful therapy for this debilitating condition."

The good news for Covid long haulers is that after 12 months, the T-cell levels of patients with severe Covid symptoms were similar to those of patients who experienced mild and moderate symptoms – suggesting that severe cases can resolve over time.