inclusion criteria: 1. have completed a primary schedule of two doses of pfizer-biontech or astrazeneca vaccines and received a booster of pfizer-biontech vaccine (30µg) at least 3 months earlier. 2. no confirmed sars-cov-2 infection on pcr or rat within the last 3 months. 3. willing and able to give written informed consent. 4. aged 18 years or above. 5. willing to complete the follow-up requirements of the study.

inclusion criteria: 1. have completed a primary schedule of two doses of pfizer-biontech or astrazeneca vaccines and received a booster of pfizer-biontech vaccine (30µg) at least 3 months earlier. 2. no confirmed sars-cov-2 infection on pcr or rat within the last 3 months. 3. willing and able to give written informed consent. 4. aged 18 years or above. 5. willing to complete the follow-up requirements of the study.

inclusion criteria: have completed a primary schedule of two doses of pfizer-biontech or astrazeneca vaccines and received a booster of pfizer-biontech vaccine (30µg) at least 3 months earlier. no confirmed sars-cov-2 infection on pcr or rat within the last 3 months. willing and able to give written informed consent. aged 18 years or above. willing to complete the follow-up requirements of the study.

inclusion criteria: have completed a primary schedule of two doses of pfizer-biontech or astrazeneca vaccines and received a booster of pfizer-biontech vaccine (30µg) at least 3 months earlier. no confirmed sars-cov-2 infection on pcr or rat within the last 3 months. willing and able to give written informed consent. aged 18 years or above. willing to complete the follow-up requirements of the study.