Recovered Volunteers (RV): Six healthy persons who have recovered from an acute SARS-CoV-2 infection. Inclusion criteria: - Participants 18 and older - Ability to provide informed consent - Completed participation in Phase B of Protocol 000089 - Met 000089 Inclusion criteria for Mild to Moderate COVID-19 without PASC symptoms: - Licensed Independent Practitioner documentation of a stable state of general well health and physical function prior to contracting SARS-CoV-2. This may include medical records, correspondence letters, or information gathered from telephone calls with study personnel. - A self-reported illness narrative of recovery to prior health after a SARS/CoV2 infection. - Laboratory documentation of a positive COVID-19 PCR, NAA, or other EUA approved test to confirm active COVID infection at the time of the SARS-CoV-2 infection. Participants with positive home tests during Phase A will be required to have a positive anti-SARS nucleocapsid antibody test. - Meets WHO Clinical Progression Scale of 2 - 6: 2: Ambulatory; symptomatic, independent 3: Ambulatory; symptomatic, assistance needed 4: Hospitalized; no oxygen therapy 5: Hospitalized; oxygen by mask or nasal prongs 6: Hospitalized; oxygen by non-invasive ventilation or high flow oxygen - Functional Criteria: No substantial symptom severity as determined using SF-36v2: score of >=85 physical function subscale, and >=85 on role physical subscale, and >=85 on social function subscale. - Determined to be a Healthy Comparator by the 000089 Case Adjudication Committee Neurologic Post-Acute Sequelae of COVID-19 Participants (Neuro-PASC): Six persons with ongoing neurological complaints following an acute SARS-CoV-2 infection. Inclusion criteria: - Participants 18 and older - Ability to provide informed consent - Completed participation in Phase B of Protocol 000089 - Met 000089 Inclusion criteria for Mild to Moderate COVID-19 without PASC symptoms: - Licensed Independent Practitioner documentation of a stable state of general well health and physical function prior to contracting SARS-CoV-2. This may include medical records, correspondence letters, or information gathered from telephone calls with study personnel. - A self-reported illness narrative of the development of persistent PASC symptoms after recovering from a SARS-CoV-2 infection. These include symptoms such as fatigue, cognitive difficulties, orthostatic intolerance, unrefreshing sleep, neuropathic pain, mood change, and post-exertional malaise. - Laboratory documentation of a positive COVID-19 PCR, NAA, or other EUA approved test to confirm active COVID infection at the time of the SARS-CoV-2 infection. Participants with positive home tests during Phase A will be required to have a positive anti-SARS nucleocapsid antibody test . - Meets WHO Clinical Progression Scale of 2 - 6: 2: Ambulatory; symptomatic, independent 3: Ambulatory; symptomatic, assistance needed 4: Hospitalized; no oxygen therapy 5: Hospitalized; oxygen by mask or nasal prongs 6: Hospitalized; oxygen by non-invasive ventilation or high flow oxygen - Functional Criteria: Substantial symptom severity as determined using SF-36v2: score of<= 70 physical function subscale, or <=50 on role physical subscale, or <=75 on social function subscale. - Determined to have Post-Acute Sequelae of COVID-19 by the 000089 Case Adjudication Committee - Primary PASC complaint is neurologic including: - Neuropathic sensations - Cognitive complaints - Postural (Orthostatic) complaints - Motor complaints

• Current suicidal ideation - Women who are pregnant, breastfeeding, or are within one-year post-partum. - Current or previous malignancy. A history of malignancy that has fully resolved with surgical resection only (e.g. no chemotherapy, radiation therapy, or immunotherapy) will be allowed. - Current systemic immunologic disorders (e.g. Type 1 diabetes, rheumatoid arthritis). Local immunological disorder (e.g. atopic dermatitis, stable autoimmune thyroid disease) and allergic disorders will be allowed. - Current or previous long-term immune suppressive therapy. Systemic steroid use, even short-term, must not have been used within the month prior to enrollment. - Long term use of anticoagulant or antiplatelet medications. - Active participation in a clinical protocol (e.g. anti-inflammatory drug intervention study) which includes an intervention that may affect the results of the current study. - Not willing to allow for research data and samples to be shared broadly with other researchers. - Employees at NIH that are under the direct supervision of the study investigators. - Symptom severity that makes it impossible for the volunteer to travel to NIH for an extended inpatient evaluation - Use of medications with a high-risk for withdrawal-related complications (i.e. long-acting opiates or benzodiazepines). - Unwillingness to co-enroll in protocol 17-I-0122: NIAID Centralized Sequencing Protocol.