Phase II / III Study of COVID-19 DNA Vaccine (AG0302-COVID19)

Inclusion Criteria: 1. Subjects who have obtained written consent voluntarily to participate in this clinical trial 2. Subjects whose age at the time of obtaining consent is 18 years or older 3. Subjects who are negative for SARS-CoV-2 by PCR test 4. Subjects who are negative for both SARS-CoV-2 IgM antibody and SARS-CoV-2 IgG antibody by antibody test Exclusion Criteria: 1. Subjects with symptoms of suspected COVID-19 infection (respiratory symptoms, headache, malaise, olfactory disorders, taste disorders, etc.) 2. Subjects with a history of COVID-19 (hearing from subjects) 3. Subjects who have participated in unapproved vaccine clinical trials within 1 year before the start of this study 4. Subjects with axillary temperature of 37.0 degree or higher at the time of screening and before the first vaccination 5. Subjects who have a history of anaphylaxis 6. Subjects who have a history of hypersensitivity to the ingredients of the investigational drug 7. Subjects who have a current or history of serious renal, cardiovascular, respiratory, liver, kidney, gastrointestinal, and neuropsychiatric diseases 8. Subjects with a history of convulsion or epilepsy 9. Subjects with a history of diagnosis of immunodeficiency 10. Subjects who have a close relative (within 3rd degree) of congenital immunodeficiency 11. Subjects who have current bronchial asthma 12. Subjects who have had a fever of 39.0 degrees or higher within 2 days after vaccination, or who have been suspected of having an allergy such as a systemic rash. 13. Females who wish to become pregnant from the study registration to 12 weeks after the first vaccination, and pregnant females who are breast-feeding. In addition, females who may become pregnant and their male sexual partners should use appropriate contraceptives (pill), condoms, vasectomy, tubal ligation, diaphragm, intrauterine devices, spermicides, intrauterine hormone-releasing system, etc. from the study entry date until 12 weeks after the first vaccination 14. Subjects who have participated in clinical trials of other unapproved drugs and received the investigational drug within 4 weeks before the start of this clinical trial (starting from vaccination day) 15. Subjects who have been received a live vaccine, inactivated vaccine, or toxoid within 4 weeks before the start of this clinical trial (starting from vaccination day) 16. Subjects who have been administered with drugs that affect the immune system (excluding external preparations) such as immunomodulators (DMARDs, etc.), immunosuppressants, biologics, etc. within 4 weeks before vaccination 17. Subjects who received blood transfusion or gamma globulin therapy within 12 weeks before vaccination, or high-dose gamma globulin therapy (200 mg/kg or more) within 24 weeks before vaccination 18. Subjects who have a history of overseas travel within 4 weeks before the start of the clinical trial (starting from vaccination day) 19. Subjects who are unable to comply with the clinical trial protocol and follow up (for mental, family, social or geographical reasons) 20. Subjects who are judged to be ineligible for this clinical trial by the investigator