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.