1. Aged 65 years old or more. 2. Having a 2-dose primary series of ChAdOx1 (AstraZeneca) vaccine for 12-24 weeks. 3. Stable and well-controlled chronic diseases. 4. Ability to understand and communicate in Thai language. 5. Ability to attend the appointment. 6.Ability to give informed consent

1. Aged 65 years old or more. 2. Having a 2-dose primary series of ChAdOx1 (AstraZeneca) vaccine for 12-24 weeks. 3. Stable and well-controlled chronic diseases. 4. Ability to understand and communicate in Thai language. 5. Ability to attend the appointment. 6.Ability to give informed consent