ChulaCov19 Vaccine in Healthy Adults

This study will be conducted as a combined phase 1/2 study in healthy participants. The first phase of the study will evaluate the safety, tolerability, and reactogenicity of escalating doses (10 µg, 25 µg, and 50 µg) of the ChulaCov19 vaccine, administered intramuscularly (IM) according to a repeat vaccination schedule (given 21 days apart) in healthy adults aged 18-55 years and in elderly adults aged 56-75 years, up to Visit 10 (Day 50 ±3). The second phase of the study will evaluate the safety, tolerability, and reactogenicity of escalating doses of the ChulaCov19 vaccine, administered intramuscularly (IM) according to a repeat vaccination schedule (given 21 days apart) in healthy adults aged 18--75 years, up to Visit 10 (Day 50 ±3). The study will also evaluate the immunogenicity measured as neutralising antibody titre (measured by Micro-viral neutralising test \[MicroVNT\]) following repeat vaccination of escalating doses of the ChulaCov19 vaccine, administered IM according to a repeat vaccination schedule (given 21 days apart) in healthy adults aged 18-75 years, at Visit 9 (Day 29 +3).