Safety and Immunogenicity of EXG-5003

Inclusion Criteria: * Has provided written consent for participation * Age between 20 and 55 * Has a negative nucleic acid-based test result for SARS-CoV-2 * Has a negative antibody test result for SARS-CoV-2 Exclusion Criteria: * Signs and symptoms consistent with COVID-19 upon screening * History of COVID-19 * Presence of uncontrolled cardiovascular, hematologic, respiratory, hepatic, renal, gastrointestinal, or neuropsychiatric disease * Presence of diabetes mellitus * Presence of active autoimmune disease * Positive for HBc, HCV or HIV antibody * History of anaphylactic shock * History of epilepsy * Presence of active malignancy * Presence of lung disease (e.g., COPD, asthma) * Positive urine pregnancy test within 24 hours * Pregnant, lactating, planned pregnancy of self (if female) or partner (if male) within 90 days after administration of the trial drug * If female and premenopausal, not agreeable to contraception for 90 days after second administration of the trial drug * If male, not agreeable to contraception for 90 days after second administration of the trial drug * Presence of clinically relevant electrocardiogram or vital sign abnormality at screening * Participated in a clinical trial of a drug or a medical device within 30 days or a biologic within 90 days * Received any SARS-CoV-2 vaccine * Received within 90 days, or is planning to receive during the study period, an immunoglobulin or blood product * Received within 180 days, or is planning to receive during the study period, a biologic product with immunosuppressive properties * Received for 14 days or more within 180 days, or is planning to receive during the study period, a corticosteroid * Deemed ineligible for the study as determined by the principal investigator or a co-investigator