Evaluation of Efficacy, Safety and Immunogenicity of GX-19N in Healthy Individuals Who Have Received COVID-19 Vaccines

Inclusion Criteria: 1. Adult males or females aged 18 years and above at the time of consent 2. Healthy subjects in normal medical condition as determined by medical history, physical examination, and investigator's discretion 3. Have previously received homologous full-dose of COVID-19 vaccine authorized for emergency use, and at least 3 months post second vaccination prior to Day 1 4. Negative results for SARS-COV-2 rapid antigen test at the screening period 5. Able to comply with all study procedures and requirements 6. Agree for blood and nasal swab samples could be collected throughout the study period, including surveillance visit Exclusion Criteria: 1. Unable to follow clinical and follow-up procedures 2. Acute fever with temperature above 38℃, coughing, breathing difficulty, chills, muscle ache, headache, sore throat, loss of smell, or loss of taste within 72 hours prior to the vaccination 3. History of SARS-CoV-2 infection or have experienced prior administration of an investigational coronavirus (SARS-CoV, MERS-CoV) vaccine 4. History of a malignant disease within the past 5 years 5. Immune dysfunction, including immunodeficiency disorder, or family history of such conditions (Except stable/well-controlled HIV-positive participants) 6. Have received immunoglobulin or blood-derived products within 3 months prior to the vaccination or are scheduled to receive them during the study period 7. Have been dependent on antipsychotic drugs and narcotic analgesics within 6 months prior to the vaccination 8. History or are suspected of alcohol or drug dependency 9. History of hypersensitivity or allergic reactions including anaphylaxis 10. A current or history of clinically significant chronic cardiovascular, endocrine, gastrointestinal, hepatic (including hepatitis B and C), renal, neurological, respiratory, psychiatric or other medical disorders not excluded by other exclusion criteria, that are assessed by the investigator 11. Hemophiliacs or people using anticoagulants who are at a risk of serious bleeding from IM injection 12. Have received or plans to receive other vaccination(s) within 28 days prior to or during study duration (except for influenza vaccine which is not allowed within 14 days before, or 4 weeks after final dose of IP) 13. Have taken an immunosuppressant or immune-modifying drug within 3 months prior to the vaccination; chronic administration (defined as more than 14 continuous days) of immunosuppressant medication within the past 3 months, except topical steroids or short-term oral steroids (course lasting ≤ 14 days) 14. Female who are pregnant or breastfeeding; however, participation is possible if breastfeeding is discontinued prior to participation in the study 15. Have received or have plans to receive other investigational drug(s) while participating in another clinical study or bioequivalence study within 28 days prior to vaccination 16. Not consent to the use of effective contraception at least 90 days after the last vaccination 17. Lack of acceptable sites available for IM injection and EP 18. Deemed ineligible by the investigator based on other clinically significant medical or psychiatric findings