Since the beginning of the pandemic, SARS-CoV-2 has been suspected of causing chronic fatigue syndrome (ME/CFS). A well-controlled study conducted by a group of researchers from Charité—Universitätsmedizin Berlin and the Max Delbrück Center for Molecular Medicine (MDC) has now shown that, even after mild COVID-19, a subset of patients will develop symptoms which meet the diagnostic criteria for ME/CFS. Their findings also describe a second subset of post-COVID patients with similar symptoms. Differences in laboratory results between these groups may indicate differences in underlying mechanisms. The researchers’ findings have been published in Nature Communications.