1. Adults aged more than 18 years. 2. Completed primary series of COVID-19 vaccine with either homologous primary vaccination with 2 doses of ChAdOx-1 or Heterologous Sinovac-AstraZeneca at least 90 days before screening heterologous primary vaccination with CoronaVac (Sinovac) following by ChAdOx-1 at least 90 days before screening 3. Has provided written informed consent prior to performance of any study-specific procedure 4. No history of fever or PUI symptoms within 7 days

1. Adults aged more than 18 years. 2. Completed primary series of COVID-19 vaccine with either homologous primary vaccination with 2 doses of ChAdOx-1 or Heterologous Sinovac-AstraZeneca at least 90 days before screening heterologous primary vaccination with CoronaVac (Sinovac) following by ChAdOx-1 at least 90 days before screening 3. Has provided written informed consent prior to performance of any study-specific procedure 4. No history of fever or PUI symptoms within 7 days