inclusion criteria: clinically healthy adults aged 18 years and above who had completed the primary series of covid-19 vaccine with coronavac or astrazeneca more than 6 months prior to enrolment to the study. signed written informed consent form and willing to comply with the instructions of the investigator and the schedule of the trial.

inclusion criteria: clinically healthy adults aged 18 years and above who had completed the primary series of covid-19 vaccine with coronavac or astrazeneca more than 6 months prior to enrolment to the study. signed written informed consent form and willing to comply with the instructions of the investigator and the schedule of the trial.