1. Participants must age 18 to 69 years old on the day of vaccination and meet either cohort inclusion criteria. o Cohort 1: Participants must age 60 to 69 years old on the day of vaccination. o Cohort 2: Participants must have underlying disease e.g., diabetes mellitus, chronic kidney disease, cardiovascular disease. o Cohort 3: Participants must be considered immunocompromised e.g., currently taking immunosuppressant, active cancer currently on treatment. o Cohort 4 (Control): Participants must age 18 to 59 years old and be in good health at the time of entry into the trial as determined by medical history, physical examination (including vital signs), and the clinical judgment of the investigator. 2. Participants must have received 2 doses of AZD1222 vaccination with interval at least 8 weeks apart. 3. Participants must have received 2nd dose of AZD1222 for more than 60 days at the day of vaccination. 4. Participants must be able to communicate effectively with study personnel and considered reliable, willing, and cooperative in terms of compliance with the protocol requirements. 5. Participants must sign a written informed consent form, including any required privacy authorization form, prior to the initiation of any trial procedures, after the nature of the trial has been explained according to local regulatory requirements.

1. Participants must age 18 to 69 years old on the day of vaccination and meet either cohort inclusion criteria. o Cohort 1: Participants must age 60 to 69 years old on the day of vaccination. o Cohort 2: Participants must have underlying disease e.g., diabetes mellitus, chronic kidney disease, cardiovascular disease. o Cohort 3: Participants must be considered immunocompromised e.g., currently taking immunosuppressant, active cancer currently on treatment. o Cohort 4 (Control): Participants must age 18 to 59 years old and be in good health at the time of entry into the trial as determined by medical history, physical examination (including vital signs), and the clinical judgment of the investigator. 2. Participants must have received 2 doses of AZD1222 vaccination with interval at least 8 weeks apart. 3. Participants must have received 2nd dose of AZD1222 for more than 60 days at the day of vaccination. 4. Participants must be able to communicate effectively with study personnel and considered reliable, willing, and cooperative in terms of compliance with the protocol requirements. 5. Participants must sign a written informed consent form, including any required privacy authorization form, prior to the initiation of any trial procedures, after the nature of the trial has been explained according to local regulatory requirements.