inclusion criteria: * healthy male or non-pregnant female between the age of 20 and 55 years at time of enrolment. * fully vaccinated with two injections of astrazeneca covid-19 vaccine (chadox1-s) with an 8-16 week interval between first and second doses. the second dose of astrazeneca covid-19 vaccine (chadox1-s) must have been administered more than six (6) months from study day 1. the cdc covid-19 vaccination record card or appropriate documentation (e.g., medical records) will be required for documentation. * women of childbearing potential and men must agree to practice medically effective contraception from vaccination until 30 days after the vaccination. * participant or the participant's legal representative must understand the procedures of the study and is willing to sign the informed consent form (icf). * able to understand and agrees to comply with all study procedures and be available for all study visits. * must be able to read, understand, and complete the protocol-required questionnaires and/or diary. * negative serological test for hepatitis b surface antigen (hbsag), hcv rna and hiv antibody * negative results of sars-cov-2 n protein igg elisa * negative result of rt-pcr screening of nasopharyngeal or throat swabs for sars-cov-2. * ear temperature ≤ 38.0°c. * indexes of hematology, biochemistry and immunology laboratory tests are within the normal ranges, or not clinically significant as judged by investigators

inclusion criteria: * healthy male or non-pregnant female between the age of 20 and 55 years at time of enrolment. * fully vaccinated with two injections of astrazeneca covid-19 vaccine (chadox1-s) with an 8-16 week interval between first and second doses. the second dose of astrazeneca covid-19 vaccine (chadox1-s) must have been administered more than six (6) months from study day 1. the cdc covid-19 vaccination record card or appropriate documentation (e.g., medical records) will be required for documentation. * women of childbearing potential and men must agree to practice medically effective contraception from vaccination until 30 days after the vaccination. * participant or the participant's legal representative must understand the procedures of the study and is willing to sign the informed consent form (icf). * able to understand and agrees to comply with all study procedures and be available for all study visits. * must be able to read, understand, and complete the protocol-required questionnaires and/or diary. * negative serological test for hepatitis b surface antigen (hbsag), hcv rna and hiv antibody * negative results of sars-cov-2 n protein igg elisa * negative result of rt-pcr screening of nasopharyngeal or throat swabs for sars-cov-2. * ear temperature ≤ 38.0°c. * indexes of hematology, biochemistry and immunology laboratory tests are within the normal ranges, or not clinically significant as judged by investigators

inclusion criteria: healthy male or non-pregnant female between the age of 20 and 55 years at time of enrolment. fully vaccinated with two injections of astrazeneca covid-19 vaccine (chadox1-s) with an 8-16 week interval between first and second doses. the second dose of astrazeneca covid-19 vaccine (chadox1-s) must have been administered more than six (6) months from study day 1. the cdc covid-19 vaccination record card or appropriate documentation (e.g., medical records) will be required for documentation. women of childbearing potential and men must agree to practice medically effective contraception from vaccination until 30 days after the vaccination. participant or the participant's legal representative must understand the procedures of the study and is willing to sign the informed consent form (icf). able to understand and agrees to comply with all study procedures and be available for all study visits. must be able to read, understand, and complete the protocol-required questionnaires and/or diary. negative serological test for hepatitis b surface antigen (hbsag), hcv rna and hiv antibody negative results of sars-cov-2 n protein igg elisa negative result of rt-pcr screening of nasopharyngeal or throat swabs for sars-cov-2. ear temperature ≤ 38.0°c. indexes of hematology, biochemistry and immunology laboratory tests are within the normal ranges, or not clinically significant as judged by investigators

inclusion criteria: healthy male or non-pregnant female between the age of 20 and 55 years at time of enrolment. fully vaccinated with two injections of astrazeneca covid-19 vaccine (chadox1-s) with an 8-16 week interval between first and second doses. the second dose of astrazeneca covid-19 vaccine (chadox1-s) must have been administered more than six (6) months from study day 1. the cdc covid-19 vaccination record card or appropriate documentation (e.g., medical records) will be required for documentation. women of childbearing potential and men must agree to practice medically effective contraception from vaccination until 30 days after the vaccination. participant or the participant's legal representative must understand the procedures of the study and is willing to sign the informed consent form (icf). able to understand and agrees to comply with all study procedures and be available for all study visits. must be able to read, understand, and complete the protocol-required questionnaires and/or diary. negative serological test for hepatitis b surface antigen (hbsag), hcv rna and hiv antibody negative results of sars-cov-2 n protein igg elisa negative result of rt-pcr screening of nasopharyngeal or throat swabs for sars-cov-2. ear temperature ≤ 38.0°c. indexes of hematology, biochemistry and immunology laboratory tests are within the normal ranges, or not clinically significant as judged by investigators

inclusion criteria: healthy male or non-pregnant female between the age of 20 and 55 years at time of enrolment. fully vaccinated with two injections of astrazeneca covid-19 vaccine (chadox1-s) with an 8-16 week interval between first and second doses. the second dose of astrazeneca covid-19 vaccine (chadox1-s) must have been administered more than six (6) months from study day 1. the cdc covid-19 vaccination record card or appropriate documentation (e.g., medical records) will be required for documentation. women of childbearing potential and men must agree to practice medically effective contraception from vaccination until 30 days after the vaccination. the acceptable effective contraception methods include: male or female sterilization, implant, or intrauterine device; injectable, pill, patch, ring plus one barrier method*; two combined barrier methods*. effective barrier methods are diaphragm, male or female condoms, sponge, or spermicides (creams or gels that contain a chemical to kill sperm). participant or the participant's legal representative must understand the procedures of the study and is willing to sign the informed consent form (icf). able to understand and agrees to comply with all study procedures and be available for all study visits. must be able to read, understand, and complete the protocol-required questionnaires and/or diary. negative serological test for hepatitis b surface antigen (hbsag), hcv rna and hiv antibody negative results of sars-cov-2 n protein igg elisa negative result of rt-pcr (reverse transcriptase pcr) screening of nasopharyngeal or throat swabs for sars-cov-2. ear temperature ≤ 38.0°c. indexes of hematology, biochemistry and immunology laboratory tests are within the normal ranges, or not clinically significant as judged by investigators

inclusion criteria: healthy male or non-pregnant female between the age of 20 and 55 years at time of enrolment. fully vaccinated with two injections of astrazeneca covid-19 vaccine (chadox1-s) with an 8-16 week interval between first and second doses. the second dose of astrazeneca covid-19 vaccine (chadox1-s) must have been administered more than six (6) months from study day 1. the cdc covid-19 vaccination record card or appropriate documentation (e.g., medical records) will be required for documentation. women of childbearing potential and men must agree to practice medically effective contraception from vaccination until 30 days after the vaccination. the acceptable effective contraception methods include: male or female sterilization, implant, or intrauterine device; injectable, pill, patch, ring plus one barrier method*; two combined barrier methods*. effective barrier methods are diaphragm, male or female condoms, sponge, or spermicides (creams or gels that contain a chemical to kill sperm). participant or the participant's legal representative must understand the procedures of the study and is willing to sign the informed consent form (icf). able to understand and agrees to comply with all study procedures and be available for all study visits. must be able to read, understand, and complete the protocol-required questionnaires and/or diary. negative serological test for hepatitis b surface antigen (hbsag), hcv rna and hiv antibody negative results of sars-cov-2 n protein igg elisa negative result of rt-pcr (reverse transcriptase pcr) screening of nasopharyngeal or throat swabs for sars-cov-2. ear temperature ≤ 38.0°c. indexes of hematology, biochemistry and immunology laboratory tests are within the normal ranges, or not clinically significant as judged by investigators