inclusion criteria: 1. 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. 2. signed written informed consent form and willing to comply with the instructions of the investigator and the schedule of the trial.

inclusion criteria: 1. 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. 2. 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.

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.