inclusion criteria: male or female participant aged 20 to 64 years at randomization. has received two doses of the chadox1-ncov-19 (astra-zeneca) 12 to 16 weeks before randomization. female participant must: be either of non-childbearing potential, i.e. surgically sterilized (defined as having undergone hysterectomy and/or bilateral oophorectomy and/or bilateral salpingectomy; tubal ligation alone is not considered sufficient) or one year post-menopausal; or, if of childbearing potential, be abstinent or agree to use medically effective contraception from 14 days before screening to 30 days following the last administration of study intervention. acceptable forms include: i.implanted hormonal methods of contraception or placement of an intrauterine device or intrauterine system ii.established use of hormonal methods (injectable, pill, patch or ring) combined with barrier methods of contraception: condom or occlusive cap (diaphragm or cervical/vault caps) with spermicidal foam/gel/film/cream/suppository c.have a negative pregnancy test participant is willing and able to comply with all required study visits and follow-up required by this protocol. participant or the participant's legal representative must understand the procedures of the study and provide written informed consent.

inclusion criteria: male or female participant aged 20 to 64 years at randomization. has received two doses of the chadox1-ncov-19 (astra-zeneca) 12 to 16 weeks before randomization. female participant must: be either of non-childbearing potential, i.e. surgically sterilized (defined as having undergone hysterectomy and/or bilateral oophorectomy and/or bilateral salpingectomy; tubal ligation alone is not considered sufficient) or one year post-menopausal; or, if of childbearing potential, be abstinent or agree to use medically effective contraception from 14 days before screening to 30 days following the last administration of study intervention. acceptable forms include: i.implanted hormonal methods of contraception or placement of an intrauterine device or intrauterine system ii.established use of hormonal methods (injectable, pill, patch or ring) combined with barrier methods of contraception: condom or occlusive cap (diaphragm or cervical/vault caps) with spermicidal foam/gel/film/cream/suppository c.have a negative pregnancy test participant is willing and able to comply with all required study visits and follow-up required by this protocol. participant or the participant's legal representative must understand the procedures of the study and provide written informed consent.

inclusion criteria: 1. male or female participant aged 20 to 64 years at randomization. 2. has received two doses of the chadox1-ncov-19 (astra-zeneca) 12 to 16 weeks before randomization. 3. female participant must: 1. be either of non-childbearing potential, i.e. surgically sterilized (defined as having undergone hysterectomy and/or bilateral oophorectomy and/or bilateral salpingectomy; tubal ligation alone is not considered sufficient) or one year post-menopausal; 2. or, if of childbearing potential, be abstinent or agree to use medically effective contraception from 14 days before screening to 30 days following the last administration of study intervention. acceptable forms include: i.implanted hormonal methods of contraception or placement of an intrauterine device or intrauterine system ii.established use of hormonal methods (injectable, pill, patch or ring) combined with barrier methods of contraception: condom or occlusive cap (diaphragm or cervical/vault caps) with spermicidal foam/gel/film/cream/suppository c.have a negative pregnancy test 4. participant is willing and able to comply with all required study visits and follow-up required by this protocol. 5. participant or the participant's legal representative must understand the procedures of the study and provide written informed consent.

inclusion criteria: 1. male or female participant aged 20 to 64 years at randomization. 2. has received two doses of the chadox1-ncov-19 (astra-zeneca) 12 to 16 weeks before randomization. 3. female participant must: 1. be either of non-childbearing potential, i.e. surgically sterilized (defined as having undergone hysterectomy and/or bilateral oophorectomy and/or bilateral salpingectomy; tubal ligation alone is not considered sufficient) or one year post-menopausal; 2. or, if of childbearing potential, be abstinent or agree to use medically effective contraception from 14 days before screening to 30 days following the last administration of study intervention. acceptable forms include: i.implanted hormonal methods of contraception or placement of an intrauterine device or intrauterine system ii.established use of hormonal methods (injectable, pill, patch or ring) combined with barrier methods of contraception: condom or occlusive cap (diaphragm or cervical/vault caps) with spermicidal foam/gel/film/cream/suppository c.have a negative pregnancy test 4. participant is willing and able to comply with all required study visits and follow-up required by this protocol. 5. participant or the participant's legal representative must understand the procedures of the study and provide written informed consent.