The primary objective of this study is to evaluate the safety and efficacy of Larazotide (AT1001) versus placebo in children and adults 7 to ≤50 years of age who present with symptoms of Long COVID in the presence of SARS-CoV-2 antigenemia. AT1001 (n=100) or placebo (n=50) will be administered orally four times a day (QID) for 21 days.

This is a Phase 2a randomized, double-blind, placebo-controlled clinical trial to evaluate the safety and efficacy of AT1001 for use in children and adults with symptoms of Long COVID. Eligible participants (N= 150) will be treated with AT1001 (n= 100) or matching placebo (n= 50) orally four times a day (QID for 21 days). The study will consist of two phases:

I. Baseline Visit and Treatment phase

After confirming subject eligibility, a licensed physician investigator will obtain informed consent. Subjects will be asked to complete baseline surveys (SBQ™-LC, PedsQL, and Symptom Severity Survey) to assess organ involvement and symptom severity. A venous blood sample will be obtained to, among other things, assess for SARS COV-2 antigenemia (such as Spike protein) and obtain a comprehensive metabolic panel and liver function test. Patients who meet inclusion criteria will be treated with AT1001 or matching placebo at a dose of 250 μg or 500 μg for 21 days. Drug dose will be determined by weight: patients <25.0 kg will receive 250 μg of Larazotide or Placebo, and patients ≥25.0 kg will receive 500 μg of Larazotide or Placebo. Randomization and initial dosing will occur on Visit 1 (Day 1). Visits will then occur on a weekly basis during the treatment phase and will consist of data and/or specimen collection. Visit 2 (Week 1) and Visit 3 (Week 2) will take place virtually and will not involve sample collection. Once the subject has completed 21 days of dosing, Visit 4 (Week 3) will take place in person and require the collection of blood, stool and nasal swabs.

II. Follow-up phase

Patients will have two additional virtual follow-up visits after completing their 21-day course of treatment with the study drug. The first follow up visit will occur one week after completing the study drug (ie. at week 4), and the second will occur one month later (ie. at week 8). Week 8 visit will serve as the end of study visit. Biospecimens will not be collected during the follow-up phase.

Safety monitoring, including physical examination, vitals, and clinical laboratory testing will be performed during the baseline phase and after completion of treatment. Adverse events and concomitant medications will be recorded during the entire study.

Total duration of the participants' participation in the study is approximately 8 weeks (with 21 days treatment period). Total duration of the study is projected to be roughly 42 months, dependent on enrollment timeline.

Inclusion Criteria:

• Age 7 to ≤50 years
• History of SARS-CoV-2 infection, documented by positive PCR and/or antigen test
• Ongoing, worsening, new, or recurrent symptoms present ≥4 weeks after SARS-CoV-2 infection.Symptoms include but are not limited to fatigue, malaise, headache, cognitive impairment, neuropsychiatric symptoms, decreased exercise tolerance, post exertional malaise, dyspnea, cough, chest pain, palpitations, tachycardia, gastrointestinal symptoms, musculoskeletal symptoms, fever, lightheadedness, insomnia and other sleep disturbances, anosmia or dysgeusia, pain, paresthesia, menstrual cycle irregularities, erectile dysfunction.

Exclusion Criteria:

• Age ≤6 years or >50 years at time of enrollment
• Pregnancy and/or lactation
• Female participant of childbearing age unwilling to use an acceptable method of birth control for the duration of the study
• Inability to tolerate drug
• Unstable medical conditions or significant co-morbid disease that, by the investigator's determination would make the participant unsuitable for enrollment
• Participation in any other clinical investigation using an experimental drug within 30 days prior to screening
• Intent to participate in another clinical study while participating in this clinical trial
• Blood/plasma donation and or blood loss greater than 400 mL within 90 days, or greater than 200 mL within 30 days prior to screening
• Known hypersensitivity to any of the formulation components of AT1001.
• Abnormal baseline liver function as indicated by AST or ALT ≥3 times the upper limit of normal (ULN), or total bilirubin ≥2x ULN for age
• Abnormal baseline renal function, defined as glomerular filtration rate ≤50 mL/min/1.73m2

Double-blind: Participant and Investigator blinded. Pharmacy unblinded.