The purpose of this study is to evaluate the safety and immunogenicity of ascending dose levels of VXCO-100 in healthy adults.

This is a phase 1, multisite clinical trial to evaluate the safety and immunogenicity of 3 dose levels of VXCO-100 in healthy adult volunteers.

Participants will be vaccinated with 1 dose of VXCO-100 on Day 1. A subset of participants will be offered an optional interim boost at month 3.

Safety will be evaluated 1) before proceeding to a higher dose level and 2) prior to enrollment of participants aged 56 years and older at a particular dose level.

Inclusion Criteria

A participant must meet all the following criteria to be eligible for the study:

• Adults ages 18 years and older.
• Judged by the investigator to be healthy based on participant-reported medical history, physical examination, vital signs, and laboratory assessment.
• Able to provide written informed consent.
• Willing to disclose prior COVID-19 vaccination status.
• Willing to disclose prior participant-reported SARS-CoV-2 infection status.
• Prior receipt of at least 3 injections with a COVID-19 mRNA vaccine with the most recent dose at least 6 months prior to enrollment.
• Willing to comply with all study procedures during the follow-up period of approximately 12 or 24 months, depending on number of doses received.
• Body mass index of ≤ 40 kg/m2 within 30 days prior to enrollment
• Electrocardiogram (ECG) without clinically significant abnormalities. Laboratory Criteria within 30 days before enrollment
• White blood cells (WBC) and differential within institutional normal range or accompanied by the site Principal Investigator (PI) or designee approval.
• Total lymphocyte count ≥ 800 cells/µL.
• Platelets between 125,000 and 500,000 cells/µL.
• Hemoglobin within institutional normal range or accompanied by the PI or designee approval.
• Alanine aminotransferase (ALT) ≤ 1.25 x institutional upper limit of normal (ULN).
• Aspartate aminotransferase (AST) ≤ 1.25 x institutional ULN.
• Serum creatinine ≤ 1.1 x institutional ULN.
• Ferritin, iron and TIBC within institutional normal range or accompanied by the PI or designee approval.

For participants of childbearing potential:

• Negative beta-human chorionic gonadotropin (β-HCG) pregnancy test (urine or serum) on the day of enrollment.
• Must agree to avoid pregnancy from 21 days prior to study Day 1 until at least 90 days after last study vaccination.

Exclusion Criteria

A participant will be excluded if one or more of the following conditions apply:

• Known SARS-CoV-2 infection or positive test result within 6 months prior to Day 1.
• Ongoing prophylactic COVID-19 treatment, or monoclonal antibody infusion within 6 months prior to Day 1.
• Any COVID-19 vaccination within 6 months prior to Day 1.
• Exhibits symptoms consistent with COVID-19 as assessed by study clinician such as: fever, dry cough, fatigue, nasal obstruction, runny nose, sore throat, myalgia, diarrhea, shortness of breath or dyspnea within 14 days prior to in Day 1.
• Known close contact (as defined by CDC, 2021a) with someone who has COVID-19 within 14 days prior to Day 1.
• History or presence of self-reported or medically documented significant medical or psychiatric condition(s) as assessed by study clinician, including:
• At high risk of severe COVID-19 disease, such as significant history of COPD or chronic lung disease, chronic kidney disease, serious heart conditions (such as heart failure, coronary artery disease or cardiomyopathies), sickle cell disease, diabetes.
• Clinically significant central nervous system disease such as epilepsy, encephalopathy, or a history of severe mental illness.
• Severe liver and/or kidney diseases, uncontrolled hypertension, or ongoing or highly likely to recur malignancies.
• Ongoing or recent clinically significant history of alcohol or drug abuse.
• Current participation in an interventional clinical study with an investigational drug/biologic/device agent or receipt of any investigational agent within 30 days prior to Day 1.
• Evidence of infection with human immunodeficiency virus (HIV), hepatitis B virus, or hepatitis C virus.
• History of myocarditis or pericarditis.
• Diagnosed with congenital or acquired immune deficiency, ongoing lymphoma, leukemia, or other clinically significant immune compromising or autoimmune conditions.
• History of known coagulation dysfunction (e.g., coagulation factor deficiency, known thrombocytopenia, platelet dysfunction, coagulation disease, etc.).
• Receipt of any live attenuated vaccine within 30 days, or with any other (non-live) vaccine within 14 days prior to Day 1.
• Received more than 10 days of any systemic immunosuppressants or cytotoxic medications within 30 days prior to Day 1, any within 14 days prior to Day 1 or is anticipating the need for immunosuppressants at any time during participation in the study.
• Received any blood products within 3 months prior to Day 1.
• Donated > 450 mL of whole blood within 30 days prior to Day 1.
• History of unexplained or recurrent anaphylaxis or angioedema, or a history of severe allergic reaction (e.g., anaphylaxis) after a previous dose of any vaccine, or to any component of the study vaccine.
• For participants of childbearing potential: breastfeeding or planning to become pregnant during trial duration.
• Any condition that, in the opinion of the investigator, would (a) pose a health risk to the participant if enrolled or (b) could interfere with evaluation of the study vaccine or interpretation of study results.