1. Males or females aged 18 years old or above. 2. Participants willing and able to comply with the study procedure. 3. Participants willing and able to provide informed consent prior to screening. 4. Participants who received two Sinovac/Butantan vaccine doses at least 4 months (120 days) prior to enrolment in this study, with a dose interval between each Sinovac/Butantan dose of 14-28 days (+ 7 days). 5. For females of childbearing potential: willingness to practice continuous effective contraception during the study and a negative pregnancy test on the day(s) of screening and vaccination.

1. Males or females aged 18 years old or above. 2. Participants willing and able to comply with the study procedure. 3. Participants willing and able to provide informed consent prior to screening. 4. Participants who received two Sinovac/Butantan vaccine doses at least 4 months (120 days) prior to enrolment in this study, with a dose interval between each Sinovac/Butantan dose of 14-28 days (+ 7 days). 5. For females of childbearing potential: willingness to practice continuous effective contraception during the study and a negative pregnancy test on the day(s) of screening and vaccination.