A Phase II clinical study of a randomized, double-blind, placebo-controlled design evaluating the administration of different doses of COVID-19 DNA vaccine in healthy adult and elderly subjects

INTERVENTION: Group 1:Test vaccine pGX9501 1.0 mg;Group 2:Test vaccine pGX9501 2.0 mg;Group 3:Placebo1.0 mg;Group 4:Placebo2.0 mg ; CONDITION: Novel Coronavirus Pneumonia (COVID‐19) PRIMARY OUTCOME: Body temperature;Adverse events;Geometric mean titers of binding antibodies against the S protein of SARS‐CoV‐2 virus (ELISA method);Geometric mean titers of neutralizing antibodies against the S protein of SARS‐CoV‐2 virus (serum neutralization assay); INCLUSION CRITERIA: 1. Complete 2 doses of pGX9501 (1.0 mg/2.0 mg) within 12 (+2) months prior to enrolling in this phase of the study screening. 2. Body mass inde X(BMI) between 18‐35 kg/m^2 (inclusive). 3. Axillary temperature <37.3 ? on the day before the third booster immunization. 4. After inquiring about the medical history and examining the results of physical examination, the researchers determined that they were healthy subjects who were in line with the immunization of this product. 5. Voluntarily participate in this clinical trial and be able to correctly understand and sign the written informed consent. 6. Be able to cooperate with the researcher, comply with the requirements of the research protocol, and complete the inspection in accordance with the relevant procedures of the protocol; agree to abide by the lifestyle specified in the research protocol during the research period (restrictions on travel abroad, business trips, travel, etc.).