Evaluation of Safety and Immunogenicity of a SARS-CoV-2(Severe Acute Respiratory Syndrome Coronavirus 2) Booster Vaccine (LEM-mR203)

Inclusion Criteria: * Healthy volunteer aged 19 years or older but less than 55 years at the time of screening. * Individuals falling into one of the following categories: * Those who have completed their primary vaccination with a domestically approved COVID-19 vaccine and have elapsed more than 90 days but less than 48 weeks since the completion of the primary vaccination. * Individuals who have completed their primary vaccination and received 1 or more additional doses; these individuals must have elapsed more than 4 months but less than 48 weeks since their last vaccination * Individuals who do not exhibit clinically significant respiratory symptoms (e.g., cough, sore throat) and do not have clinically significant active lesions on chest X-ray. * Individuals who agree to use medically accepted contraceptive methods during the entire study period before clinical trials * Individuals who agree not to donate blood or receive blood transfusions (including whole blood, plasma components, platelet components, and platelet plasma components) during the study period before clinical trials. * Individuals who can participate in all study visit schedules and comply with all study procedures. * Individuals who, after receiving detailed explanations about the clinical trial and fully comprehending it, voluntarily decide to participate, and provide written consent before the screening procedure. Exclusion Criteria: * Within 72 hours before administration of the investigational medicinal product, individuals with clinically significant respiratory symptoms (e.g., cough, sore throat), acute febrile illness with body temperature exceeding 38℃, suspicion of other infectious diseases, or individuals with symptoms suspected to be caused by other infectious diseases. * Individuals who tested positive for SARS-CoV-2 genetic test (RT-PCR) or rapid antigen test during the screening. * Individuals who have not elapsed 90 days since being diagnosed with COVID-19. * Individuals with positive results in screening tests for Hepatitis B, Hepatitis C, Syphilis (RPR), or HIV conducted during the screening. * Individuals with a smoking history within 12 weeks prior to administration of the investigational medicinal product or current smokers (smoking up to 10 cigarettes/month may be allowed based on the investigator's judgment ). * Individuals with a history of malignant tumors within 5 years before administration of the investigational medicinal product. * Individuals with a history of generalized urticaria within 5 years before administration of the investigational medicinal product. * Individuals with clinically significant conditions or medical history (e.g., respiratory diseases such as asthma, chronic obstructive pulmonary disease, active tuberculosis; cardiovascular diseases such as congestive heart failure, myocardial infarction, coronary artery disease, uncontrolled hypertension; gastrointestinal diseases such as chronic liver disease, inflammatory bowel disease; hematological and neoplastic diseases, endocrine diseases such as diabetes, hyperthyroidism; genitourinary diseases such as chronic urinary tract infections, chronic renal failure; musculoskeletal diseases such as muscular dystrophy; neurological and psychiatric diseases such as epilepsy, mood disorders, obsessive-compulsive disorder), not limited to the mentioned examples. * Individuals with a history of solid organ or bone marrow transplantation. * Individuals with a history of congenital or acquired immunodeficiency diseases or autoimmune diseases. * Participants who have received any other vaccines within 4 weeks prior to the investigational medicinal product or who have planned to receive other vaccines within 28 days after the administration of the investigational medicinal product are excluded. However, exception applies to influenza vaccines