This study investigates the use of transcutaneous vagus nerve stimulation (tVNS) for patients who have post-acute sequelae of SARS-CoV-2 infection (PASC) and meet the criteria for myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). PASC refers to long-term symptoms following a COVID-19 infection, and ME/CFS is a condition characterized by severe fatigue and other symptoms. The purpose of this study is to compare two different sets of tVNS parameters to determine which one best improves the quality of life for these patients over a 6-week period.

Participants will be assigned to one of two treatment arms and will use a device for 35 minutes each morning for 6 weeks. During the fifth week, participants will use a stick-on device to measure heart rate variability, an objective measure of treatment success. They will complete questionnaires about their symptoms and must use the device for at least 30 out of 42 days to qualify for an additional 6-week treatment with the best-performing device.

• Who can participate: Adults who have had COVID-19 and meet the 2015 case definition for ME/CFS are eligible. Participants must have a Chalder Fatigue Scale score of 4 or greater and certain symptom severity scores. Individuals with a BMI of 30 or higher, those who were hospitalized for COVID-19, or who are pregnant are excluded.
• Study details: Participants use the device for 35 minutes each morning for a 6-week period and complete questionnaires about their symptoms and functional status. A placebo is not used, as all participants receive active treatment.
• Study Timelines: The study will last 6 weeks, with a potential additional 6-week period for further treatment.