In order to be eligible to participate in this study, an individual must meet all of the following criteria: - Stated willingness to comply with all study procedures and availability for the duration of the study. - Male or female, aged at least 18 and older. - Enrolled in the screening phase of Protocol 000089 Post-Coronavirus Disease 19 Convalescence at the National Institutes of Health. - Previously diagnosed with mild-moderate COVID-19 (WHO Clinical Progression Scale between 2-5. Patients with severe acute COVID-19 requiring hospitalization or ICU care are excluded. Enrollment could take place 12 weeks after the diagnosis of acute COVID-19. - Prior COVID-19 diagnosis confirmed by patient reported infection followed by confirmatory nucleocapsid antibody testing or a positive SARS-CoV-2 PCR test result from the time of infection. - Exhibiting persistent neurologic symptoms evidenced by 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, and any ongoing issues with gait instability, vision, speech, swallowing, sensation or strength. - Non-negligible PASC symptom severity, as determined using PCFS (minimal score of 2). - Ability of subject to understand and the willingness to sign a written informed consent document. - Prior completion of a clinical brain MRI after the diagnosis of COVID-19, or willingness to complete a brain MRI. - Meets current Clinical Center HES policy for discontinuing isolation and quarantine for COVID-19.

An individual who meets any of the following criteria will be excluded from participation in this study: - For participants who have not completed a brain MRI since onset of symptoms: inability to complete brain MRI with gadolinium including contraindicated metal in the body, prior allergic reaction to gadolinium, eGFR <45 mmol/L, pregnancy or lactation, or claustrophobia that is unable to be adequately treated with a low dose oral benzodiazepine. - Contraindication to a research lumbar puncture, including use of anticoagulant medication, platelets < 50,000/uL, PT or PTT >1.5 x ULN for the NIH Clinical Center, or otherwise inability to complete the procedure. - A condition that would significantly confound interpretation of the clinical and research tests as determined by the study investigators. This could include: traumatic brain injury, substance use disorder, active malignancy, systemic immunologic disorders, current or previous long-term immune suppressive therapy. - Received a SARS-CoV-2 vaccine dose within less than 4 weeks of enrollment or is planning for any additional vaccines during the course of the study. - Prior experimental treatment for PASC with immunoglobulins. - Current medications include oral steroids or other immunosuppressive medications. - Active participation in a clinical protocol which includes any intervention that may affect the results of the current study. - Contraindication of intravenous immunoglobulins, including: - Renal insufficiency (eGFR<45mmol/L) - IgA deficiency - History of ischemic heart disease - Peripheral vascular disease - Cerebrovascular disease - Previously diagnosed hypercoagulability syndrome including antiphospholipid antibody syndrome, Protein C/S deficiency, Factor V Leiden, Antithrombin deficiency, MTHFR homozygosity - Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) greater than 3.0 times the upper limit of normal.precluding the use of acetaminophen. - Previously documented anaphylaxis or severe systemic reaction to immunoglobulins, acetaminophen, or diphenhydramine. - A severe psychiatric condition, which based on the assessment of the study investigators, will impact the ability to complete the 12-week study course. Exclusions for Optional Procedures: - Contraindication to Autonomic Testing: Refractory ventricular arrhythmias or symptomatic coronary artery disease. Daily use of medications that would impact autonomic testing (e.g. beta-blockers).