Chronic fatigue syndrome, also known as myalgic encephalomyelitis (ME/CFS), is a debilitating illness that often begins after a flu-like infection. It leaves patients with persistent symptoms such as fatigue, cognitive problems, disrupted sleep, and pain.

During the COVID-19 pandemic, a similar condition called "long COVID" emerged. Many individuals recovering from acute COVID-19 experienced lingering symptoms resembling those of ME/CFS, including fatigue, cognitive difficulties, and muscle pain. Interestingly, both ME/CFS and long COVID share not only symptoms but also underlying biological abnormalities.

These abnormalities affect various systems in the body. Neurologically, both conditions are associated with cognitive deficits, reduced blood flow in the brain, sleep problems, and autonomic dysfunction.

Immunologically and infectiously, increased levels of inflammatory markers, presence of autoantibodies, reactivation of herpesviruses, and imbalances in the gut microbiome are common. Metabolic abnormalities, including reduced energy production and increased oxidative stress, are also observed. Furthermore, cardiovascular and cardiopulmonary issues, such as diminished exercise capacity and endothelial dysfunction, are present in both conditions.