main part: 1. participants who received any other sars-cov-2 vaccine (except for the specified mrna vaccine) or other experimental novel coronavirus vaccine prior to the trial. 2. participant who received a booster vaccination (i.e. 3rd dose) 3. participants who have close contact of anyone known to have covid-19 within 14 days prior to the trial vaccination. 4. participants who were tested positive for sars-cov-2 prior to the trial. 5. participants who have traveled outside of japan in the 30 days prior to the trial participation. 6. participants with a clinically significant active infection or oral temperature \>= 38 degree celsius within 3 days of the intended date of the first single booster vaccination. 7. participants with body mass index (bmi) greater than or equal to 30 kg/m\^2 (bmi= weight in kg/ height in meters\^2) extension part: 8. participants with a clinically significant active infection or oral temperature \>=38 degree celsius within 3 days of the intended date of the second single booster vaccination.

main part: 1. participants who received any other sars-cov-2 vaccine (except for the specified mrna vaccine) or other experimental novel coronavirus vaccine prior to the trial. 2. participant who received a booster vaccination (i.e. 3rd dose) 3. participants who have close contact of anyone known to have covid-19 within 14 days prior to the trial vaccination. 4. participants who were tested positive for sars-cov-2 prior to the trial. 5. participants who have traveled outside of japan in the 30 days prior to the trial participation. 6. participants with a clinically significant active infection or oral temperature \>= 38 degree celsius within 3 days of the intended date of the first single booster vaccination. 7. participants with body mass index (bmi) greater than or equal to 30 kg/m\^2 (bmi= weight in kg/ height in meters\^2) extension part: 8. participants with a clinically significant active infection or oral temperature \>=38 degree celsius within 3 days of the intended date of the second single booster vaccination.

main part: participants who received any other sars-cov-2 vaccine (except for the specified mrna vaccine) or other experimental novel coronavirus vaccine prior to the trial. participant who received a booster vaccination (i.e. 3rd dose) participants who have close contact of anyone known to have covid-19 within 14 days prior to the trial vaccination. participants who were tested positive for sars-cov-2 prior to the trial. participants who have traveled outside of japan in the 30 days prior to the trial participation. participants with a clinically significant active infection or oral temperature >= 38 degree celsius within 3 days of the intended date of the first single booster vaccination. participants with body mass index (bmi) greater than or equal to 30 kg/m^2 (bmi= weight in kg/ height in meters^2) extension part: participants with a clinically significant active infection or oral temperature >=38 degree celsius within 3 days of the intended date of the second single booster vaccination.

main part: participants who received any other sars-cov-2 vaccine (except for the specified mrna vaccine) or other experimental novel coronavirus vaccine prior to the trial. participant who received a booster vaccination (i.e. 3rd dose) participants who have close contact of anyone known to have covid-19 within 14 days prior to the trial vaccination. participants who were tested positive for sars-cov-2 prior to the trial. participants who have traveled outside of japan in the 30 days prior to the trial participation. participants with a clinically significant active infection or oral temperature >= 38 degree celsius within 3 days of the intended date of the first single booster vaccination. participants with body mass index (bmi) greater than or equal to 30 kg/m^2 (bmi= weight in kg/ height in meters^2) extension part: participants with a clinically significant active infection or oral temperature >=38 degree celsius within 3 days of the intended date of the second single booster vaccination.

participants who received any other sars-cov-2 vaccine (except for the specified mrna vaccine) or other experimental novel coronavirus vaccine prior to the trial. participant who received a booster vaccination (i.e. 3rd dose) participants who have close contact of anyone known to have covid-19 within 14 days prior to the trial vaccination. participants who were tested positive for sars-cov-2 prior to the trial. participants who have traveled outside of japan in the 30 days prior to the trial participation. participants with a clinically significant active infection or oral temperature >= 38 degree celsius within 3 days of the intended date of vaccination. participants with body mass index (bmi) greater than or equal to 30 kg/m^2 (bmi= weight in kg/ height in meters^2)

participants who received any other sars-cov-2 vaccine (except for the specified mrna vaccine) or other experimental novel coronavirus vaccine prior to the trial. participant who received a booster vaccination (i.e. 3rd dose) participants who have close contact of anyone known to have covid-19 within 14 days prior to the trial vaccination. participants who were tested positive for sars-cov-2 prior to the trial. participants who have traveled outside of japan in the 30 days prior to the trial participation. participants with a clinically significant active infection or oral temperature >= 38 degree celsius within 3 days of the intended date of vaccination. participants with body mass index (bmi) greater than or equal to 30 kg/m^2 (bmi= weight in kg/ height in meters^2)