Study to Investigate the Efficacy of Abrocitinib in Adult Participants With Severe Fatigue From Post COVID Condition/Long COVID

Inclusion Criteria: * History of confirmed COVID-19 infection * PCC diagnosis according to the WHO definition as occurring in individuals with a history of probable or confirmed SARS CoV-2 infection, usually 3 months from the onset of COVID-19 that lasts for at least 2 months and cannot be explained by an alternative diagnosis * Participants who are willing and able to comply with all scheduled visits, treatment plan, laboratory tests, lifestyle considerations, and other study procedures * Capable of giving signed informed consent Exclusion Criteria: * Participants with acute and chronic infections, history of specific recurrent infections * Suspected or confirmed active SARS-CoV-2 infection within past 30 days * Some cardiac conditions * Any current tobacco smoker or person who has smoked tobacco products within 12 months of screening, or former tobacco smoker ≥ 50 years old * Known to be infected with Human Immunodeficiency Virus (HIV), Hepatitis B, or Hepatitis C, Herpes Virus, or Tuberculosis * History of immunodeficiency * Blood clotting conditions * Must meet general screening laboratory criteria * Allergy or other contraindication to any of the components of the study intervention * Known prior participation in this trial or other trial involving abrocitinib * Concurrent therapy with a JAK or TYK2 inhibitor * Other protocol criteria apply