inclusion criteria: * healthy adults aged 18 years and above, who have received 2 prior doses of coronavac® with an interval between those doses of 21-56 days, with the second dose given 5-8 months prior to the day of vaccination in the present study; * the participants are able to understand and sign the informed consent voluntarily; * female participants who have a negative pregnancy test on the day of vaccination, and not currently breastfeeding; * must be willing to provide verifiable identification (in accordance with the local regulations), has means to be contacted and to contact the investigator during the study.

inclusion criteria: * healthy adults aged 18 years and above, who have received 2 prior doses of coronavac® with an interval between those doses of 21-56 days, with the second dose given 5-8 months prior to the day of vaccination in the present study; * the participants are able to understand and sign the informed consent voluntarily; * female participants who have a negative pregnancy test on the day of vaccination, and not currently breastfeeding; * must be willing to provide verifiable identification (in accordance with the local regulations), has means to be contacted and to contact the investigator during the study.

inclusion criteria: healthy adults aged 18 years and above, who have received 2 prior doses of coronavac® with an interval between those doses of 21-56 days, with the second dose given 5-8 months prior to the day of vaccination in the present study; the participants are able to understand and sign the informed consent voluntarily; female participants who have a negative pregnancy test on the day of vaccination, and not currently breastfeeding; must be willing to provide verifiable identification (in accordance with the local regulations), has means to be contacted and to contact the investigator during the study.

inclusion criteria: healthy adults aged 18 years and above, who have received 2 prior doses of coronavac® with an interval between those doses of 21-56 days, with the second dose given 5-8 months prior to the day of vaccination in the present study; the participants are able to understand and sign the informed consent voluntarily; female participants who have a negative pregnancy test on the day of vaccination, and not currently breastfeeding; must be willing to provide verifiable identification (in accordance with the local regulations), has means to be contacted and to contact the investigator during the study.