inclusion criteria: * for cohorts 1 and 2, have received astrazeneca's azd1222 covid-19 prime and boost vaccine (covishield®, vaxzevria®), with the last dose received at least 2 months or more prior to day 1. * for cohort 3, have received a primary series of an adenoviral (astrazeneca azd1222 \[covishield®, vaxzevria®\] or janssen \[janssen covid-19 vaccine\]) covid-19 vaccine (under emergency supply procedures or upon full approval and may have received booster doses of an authorized vaccine), with the last dose received at least 2 months or more prior to day 1. * for cohorts 4 and 6, have received a primary series of an mrna (pfizer/biontech \[comirnaty®\] or moderna \[spikevax®\]) covid-19 vaccine (under emergency supply procedures or upon full approval and may have received booster doses of an authorized vaccine), with the last dose received at least 2 months or more prior to day 1. * agree to refrain from blood donation during the course of the study. * women of childbearing potential (wocbp)\* must agree to avoid pregnancy and be willing to use a highly effective method of contraception\*\* consistently for 30 days prior to the first study vaccine and for at least 60 days after the last study vaccine * male subjects of childbearing potential must agree to the use of condoms to ensure effective contraception with a female partner from the time of study vaccination until 3 months after vaccination. male subjects agree to refrain from sperm donation from the time of first vaccination until 3 months after the last vaccination. male subjects of childbearing potential are biological males who are post-pubertal and considered fertile until permanently sterile by bilateral orchiectomy or vasectomy. * plan to remain living in the area for the duration of the study.

inclusion criteria: * for cohorts 1 and 2, have received astrazeneca's azd1222 covid-19 prime and boost vaccine (covishield®, vaxzevria®), with the last dose received at least 2 months or more prior to day 1. * for cohort 3, have received a primary series of an adenoviral (astrazeneca azd1222 \[covishield®, vaxzevria®\] or janssen \[janssen covid-19 vaccine\]) covid-19 vaccine (under emergency supply procedures or upon full approval and may have received booster doses of an authorized vaccine), with the last dose received at least 2 months or more prior to day 1. * for cohorts 4 and 6, have received a primary series of an mrna (pfizer/biontech \[comirnaty®\] or moderna \[spikevax®\]) covid-19 vaccine (under emergency supply procedures or upon full approval and may have received booster doses of an authorized vaccine), with the last dose received at least 2 months or more prior to day 1. * agree to refrain from blood donation during the course of the study. * women of childbearing potential (wocbp)\* must agree to avoid pregnancy and be willing to use a highly effective method of contraception\*\* consistently for 30 days prior to the first study vaccine and for at least 60 days after the last study vaccine * male subjects of childbearing potential must agree to the use of condoms to ensure effective contraception with a female partner from the time of study vaccination until 3 months after vaccination. male subjects agree to refrain from sperm donation from the time of first vaccination until 3 months after the last vaccination. male subjects of childbearing potential are biological males who are post-pubertal and considered fertile until permanently sterile by bilateral orchiectomy or vasectomy. * plan to remain living in the area for the duration of the study.

inclusion criteria: * for cohorts 1 and 2, have received astrazeneca's covid-19 prime and boost vaccine at least 2 months prior to study participation. * for cohort 3, have previously received janssen/johnson and johnson or astrazeneca vaccine with or without booster dose(s) of an authorized vaccine at least 2 months prior to day 1. * for cohorts 4 and 6, have previously received an mrna covid-19 vaccine with or without booster dose(s) of an authorized vaccine with the last dose received at least 2 months prior to day 1. * agree to refrain from blood donation during the course of the study. * women of childbearing potential (wocbp)\* must agree to avoid pregnancy and be willing to use a highly effective method of contraception\*\* consistently for 30 days prior to the first study vaccine and for at least 60 days after the last study vaccine * male participants of childbearing potential must agree to the use of condoms to ensure effective contraception with a female partner from the time of study vaccination until 3 months after vaccination. * plan to remain living in the area for the duration of the study.

inclusion criteria: * for cohorts 1 and 2, have received astrazeneca's covid-19 prime and boost vaccine at least 2 months prior to study participation. * for cohort 3, have previously received janssen/johnson and johnson or astrazeneca vaccine with or without booster dose(s) of an authorized vaccine at least 2 months prior to day 1. * for cohorts 4 and 6, have previously received an mrna covid-19 vaccine with or without booster dose(s) of an authorized vaccine with the last dose received at least 2 months prior to day 1. * agree to refrain from blood donation during the course of the study. * women of childbearing potential (wocbp)\* must agree to avoid pregnancy and be willing to use a highly effective method of contraception\*\* consistently for 30 days prior to the first study vaccine and for at least 60 days after the last study vaccine * male participants of childbearing potential must agree to the use of condoms to ensure effective contraception with a female partner from the time of study vaccination until 3 months after vaccination. * plan to remain living in the area for the duration of the study.

inclusion criteria: for cohorts 1 and 2, have received astrazeneca's covid-19 prime and boost vaccine at least 2 months prior to study participation. for cohort 3, have previously received janssen/johnson and johnson or astrazeneca vaccine with or without booster dose(s) of an authorized vaccine at least 2 months prior to day 1. for cohorts 4 and 6, have previously received an mrna covid-19 vaccine with or without booster dose(s) of an authorized vaccine with the last dose received at least 2 months prior to day 1. agree to refrain from blood donation during the course of the study. women of childbearing potential (wocbp)* must agree to avoid pregnancy and be willing to use a highly effective method of contraception** consistently for 30 days prior to the first study vaccine and for at least 60 days after the last study vaccine male participants of childbearing potential must agree to the use of condoms to ensure effective contraception with a female partner from the time of study vaccination until 3 months after vaccination. plan to remain living in the area for the duration of the study.

inclusion criteria: for cohorts 1 and 2, have received astrazeneca's covid-19 prime and boost vaccine at least 2 months prior to study participation. for cohort 3, have previously received janssen/johnson and johnson or astrazeneca vaccine with or without booster dose(s) of an authorized vaccine at least 2 months prior to day 1. for cohorts 4 and 6, have previously received an mrna covid-19 vaccine with or without booster dose(s) of an authorized vaccine with the last dose received at least 2 months prior to day 1. agree to refrain from blood donation during the course of the study. women of childbearing potential (wocbp)* must agree to avoid pregnancy and be willing to use a highly effective method of contraception** consistently for 30 days prior to the first study vaccine and for at least 60 days after the last study vaccine male participants of childbearing potential must agree to the use of condoms to ensure effective contraception with a female partner from the time of study vaccination until 3 months after vaccination. plan to remain living in the area for the duration of the study.

inclusion criteria: for cohorts 1 and 2, have received astrazeneca's covid-19 prime and boost vaccine at least 2 months prior to study participation. for cohorts 3 and 5, have previously received janssen/johnson and johnson or astrazeneca vaccine with or without booster dose(s) of an authorized vaccine at least 2 months prior to day 1. for cohorts 4 and 6, have previously received an mrna covid-19 vaccine with or without booster dose(s) of an authorized vaccine with the last dose received at least 2 months prior to day 1. agree to refrain from blood donation during the course of the study. women of childbearing potential (wocbp)* must agree to avoid pregnancy and be willing to use a highly effective method of contraception** consistently for 30 days prior to the first study vaccine and for at least 60 days after the last study vaccine male participants of childbearing potential must agree to the use of condoms to ensure effective contraception with a female partner from the time of study vaccination until 3 months after vaccination. plan to remain living in the area for the duration of the study.

inclusion criteria: for cohorts 1 and 2, have received astrazeneca's covid-19 prime and boost vaccine at least 2 months prior to study participation. for cohorts 3 and 5, have previously received janssen/johnson and johnson or astrazeneca vaccine with or without booster dose(s) of an authorized vaccine at least 2 months prior to day 1. for cohorts 4 and 6, have previously received an mrna covid-19 vaccine with or without booster dose(s) of an authorized vaccine with the last dose received at least 2 months prior to day 1. agree to refrain from blood donation during the course of the study. women of childbearing potential (wocbp)* must agree to avoid pregnancy and be willing to use a highly effective method of contraception** consistently for 30 days prior to the first study vaccine and for at least 60 days after the last study vaccine male participants of childbearing potential must agree to the use of condoms to ensure effective contraception with a female partner from the time of study vaccination until 3 months after vaccination. plan to remain living in the area for the duration of the study.

inclusion criteria: have received astrazeneca's covid-19 prime and boost vaccine at least 2 months prior to study participation. agree to refrain from blood donation during the course of the study. male participants of childbearing potential must agree to the use of condoms to ensure effective contraception with a female partner from the time of study vaccination until 3 months after vaccination. plan to remain living in the area for the duration of the study.

inclusion criteria: have received astrazeneca's covid-19 prime and boost vaccine at least 2 months prior to study participation. agree to refrain from blood donation during the course of the study. male participants of childbearing potential must agree to the use of condoms to ensure effective contraception with a female partner from the time of study vaccination until 3 months after vaccination. plan to remain living in the area for the duration of the study.

inclusion criteria: for cohorts 1 and 2, have received astrazeneca's covid-19 prime and boost vaccine at least 2 months prior to study participation. for cohort 3, have previously received 2 or 3 doses of astrazeneca's covid-19 vaccine or 1 or 2 doses of johnson & johnson covid-19 vaccine with the last dose received at least 2 months prior to day 1. for cohort 4, have previously received 2 or 3 doses of an mrna covid-19 vaccine with the last dose received at least 2 months prior to day 1. agree to refrain from blood donation during the course of the study. male participants of childbearing potential must agree to the use of condoms to ensure effective contraception with a female partner from the time of study vaccination until 3 months after vaccination. plan to remain living in the area for the duration of the study.

inclusion criteria: for cohorts 1 and 2, have received astrazeneca's covid-19 prime and boost vaccine at least 2 months prior to study participation. for cohort 3, have previously received 2 or 3 doses of astrazeneca's covid-19 vaccine or 1 or 2 doses of johnson & johnson covid-19 vaccine with the last dose received at least 2 months prior to day 1. for cohort 4, have previously received 2 or 3 doses of an mrna covid-19 vaccine with the last dose received at least 2 months prior to day 1. agree to refrain from blood donation during the course of the study. male participants of childbearing potential must agree to the use of condoms to ensure effective contraception with a female partner from the time of study vaccination until 3 months after vaccination. plan to remain living in the area for the duration of the study.