inclusion criteria: 1. must be a male or female aged 18 - 64 (inclusive) at the time of enrolment 2. must have completed a primary course of 2 doses of any approved covid-19 vaccine and 3 months or more have passed since receipt of last booster dose (1 or 2 prior booster doses for a total of 3 or 4 doses) as described in table 1 3. must be able to communicate effectively with study personnel and considered reliable, willing, and cooperative in terms of compliance with the protocol requirements 4. participants must sign the written informed consent form prior to undertaking any protocol-related procedures 5. sars-cov-2 rapid antigen test is negative at day 1 (the day of receiving the study booster dose) 6. does not intend to receive any other authorized/approved covid-19 vaccine at the time of enrolment and up to 3 months of the study 7. males must be surgically sterile (\>30 days since vasectomy with no viable sperm), practice true abstinence or, if engaged in sexual relations with a female of childbearing potential, the participants and their partner must use an acceptable, highly effective, dual contraceptive method\* from screening and for a period of at least 90 days after vaccination 8. a female participant is eligible if she is not pregnant, or breastfeeding indicated by one of the following conditions: 1. with childbearing potential: she agrees to use an effective contraceptive method or abstinence from at least 4 weeks prior to the study intervention administration until at least 90 days after the study intervention administration, or 2. with non-childbearing potential. to be considered of non-childbearing potential, a female must be post-menopausal for at least 1 year or surgically sterile. if the participant is \< 1 year post-menopausal, an fsh test may be conducted to establish childbearing potential. 9. participants must be in general good health\* based on medical history and physical examination, as determined by the pi at screening. 10. participants must agree to refrain from donating blood, plasma, ova, sperm, or organs during the whole study.

inclusion criteria: 1. must be a male or female aged 18 - 64 (inclusive) at the time of enrolment 2. must have completed a primary course of 2 doses of any approved covid-19 vaccine and 3 months or more have passed since receipt of last booster dose (1 or 2 prior booster doses for a total of 3 or 4 doses) as described in table 1 3. must be able to communicate effectively with study personnel and considered reliable, willing, and cooperative in terms of compliance with the protocol requirements 4. participants must sign the written informed consent form prior to undertaking any protocol-related procedures 5. sars-cov-2 rapid antigen test is negative at day 1 (the day of receiving the study booster dose) 6. does not intend to receive any other authorized/approved covid-19 vaccine at the time of enrolment and up to 3 months of the study 7. males must be surgically sterile (\>30 days since vasectomy with no viable sperm), practice true abstinence or, if engaged in sexual relations with a female of childbearing potential, the participants and their partner must use an acceptable, highly effective, dual contraceptive method\* from screening and for a period of at least 90 days after vaccination 8. a female participant is eligible if she is not pregnant, or breastfeeding indicated by one of the following conditions: 1. with childbearing potential: she agrees to use an effective contraceptive method or abstinence from at least 4 weeks prior to the study intervention administration until at least 90 days after the study intervention administration, or 2. with non-childbearing potential. to be considered of non-childbearing potential, a female must be post-menopausal for at least 1 year or surgically sterile. if the participant is \< 1 year post-menopausal, an fsh test may be conducted to establish childbearing potential. 9. participants must be in general good health\* based on medical history and physical examination, as determined by the pi at screening. 10. participants must agree to refrain from donating blood, plasma, ova, sperm, or organs during the whole study.

inclusion criteria: must be a male or female aged 18 - 64 (inclusive) at the time of enrolment must have completed a primary course of 2 doses of any approved covid-19 vaccine and 3 months or more have passed since receipt of last booster dose (1 or 2 prior booster doses for a total of 3 or 4 doses) as described in table 1 must be able to communicate effectively with study personnel and considered reliable, willing, and cooperative in terms of compliance with the protocol requirements participants must sign the written informed consent form prior to undertaking any protocol-related procedures sars-cov-2 rapid antigen test is negative at day 1 (the day of receiving the study booster dose) does not intend to receive any other authorized/approved covid-19 vaccine at the time of enrolment and up to 3 months of the study males must be surgically sterile (>30 days since vasectomy with no viable sperm), practice true abstinence or, if engaged in sexual relations with a female of childbearing potential, the participants and their partner must use an acceptable, highly effective, dual contraceptive method* from screening and for a period of at least 90 days after vaccination a female participant is eligible if she is not pregnant, or breastfeeding indicated by one of the following conditions: with childbearing potential: she agrees to use an effective contraceptive method or abstinence from at least 4 weeks prior to the study intervention administration until at least 90 days after the study intervention administration, or with non-childbearing potential. to be considered of non-childbearing potential, a female must be post-menopausal for at least 1 year or surgically sterile. if the participant is < 1 year post-menopausal, an fsh test may be conducted to establish childbearing potential. participants must be in general good health* based on medical history and physical examination, as determined by the pi at screening. participants must agree to refrain from donating blood, plasma, ova, sperm, or organs during the whole study.

inclusion criteria: must be a male or female aged 18 - 64 (inclusive) at the time of enrolment must have completed a primary course of 2 doses of any approved covid-19 vaccine and 3 months or more have passed since receipt of last booster dose (1 or 2 prior booster doses for a total of 3 or 4 doses) as described in table 1 must be able to communicate effectively with study personnel and considered reliable, willing, and cooperative in terms of compliance with the protocol requirements participants must sign the written informed consent form prior to undertaking any protocol-related procedures sars-cov-2 rapid antigen test is negative at day 1 (the day of receiving the study booster dose) does not intend to receive any other authorized/approved covid-19 vaccine at the time of enrolment and up to 3 months of the study males must be surgically sterile (>30 days since vasectomy with no viable sperm), practice true abstinence or, if engaged in sexual relations with a female of childbearing potential, the participants and their partner must use an acceptable, highly effective, dual contraceptive method* from screening and for a period of at least 90 days after vaccination a female participant is eligible if she is not pregnant, or breastfeeding indicated by one of the following conditions: with childbearing potential: she agrees to use an effective contraceptive method or abstinence from at least 4 weeks prior to the study intervention administration until at least 90 days after the study intervention administration, or with non-childbearing potential. to be considered of non-childbearing potential, a female must be post-menopausal for at least 1 year or surgically sterile. if the participant is < 1 year post-menopausal, an fsh test may be conducted to establish childbearing potential. participants must be in general good health* based on medical history and physical examination, as determined by the pi at screening. participants must agree to refrain from donating blood, plasma, ova, sperm, or organs during the whole study.

inclusion criteria: must be a male or female aged 18 - 64 (inclusive) at the time of enrolment must have completed a primary course of 2 doses of any approved covid-19 vaccine and 3 months or more have passed since receipt of last booster dose as described in table 1 must be able to communicate effectively with study personnel and considered reliable, willing, and cooperative in terms of compliance with the protocol requirements participants must sign the written informed consent form prior to undertaking any protocol-related procedures sars-cov-2 rapid antigen test is negative at day 1 (the day of receiving the study booster dose) does not intend to receive any other authorized/approved covid-19 vaccine at the time of enrolment and up to 3 months of the study males must be surgically sterile (>30 days since vasectomy with no viable sperm), practice true abstinence or, if engaged in sexual relations with a female of child-bearing potential, the participants and their partner must use an acceptable, highly effective, double-barrier contraceptive method* from screening and for a period of at least 60 days after vaccination a female participant is eligible if she is not pregnant, or breastfeeding indicated by one of the following conditions: with childbearing potential: she agrees to use an effective contraceptive method or abstinence from at least 4 weeks prior to the study intervention administration until at least 12 weeks after the study intervention administration, or with non-childbearing potential. to be considered of non-childbearing potential, a female must be post-menopausal for at least 1 year or surgically sterile participants must be in general good health* based on medical history and physical examination, as determined by the pi at screening. participants must agree to refrain from donating blood, plasma, ova, sperm, or organs during the whole study.

inclusion criteria: must be a male or female aged 18 - 64 (inclusive) at the time of enrolment must have completed a primary course of 2 doses of any approved covid-19 vaccine and 3 months or more have passed since receipt of last booster dose as described in table 1 must be able to communicate effectively with study personnel and considered reliable, willing, and cooperative in terms of compliance with the protocol requirements participants must sign the written informed consent form prior to undertaking any protocol-related procedures sars-cov-2 rapid antigen test is negative at day 1 (the day of receiving the study booster dose) does not intend to receive any other authorized/approved covid-19 vaccine at the time of enrolment and up to 3 months of the study males must be surgically sterile (>30 days since vasectomy with no viable sperm), practice true abstinence or, if engaged in sexual relations with a female of child-bearing potential, the participants and their partner must use an acceptable, highly effective, double-barrier contraceptive method* from screening and for a period of at least 60 days after vaccination a female participant is eligible if she is not pregnant, or breastfeeding indicated by one of the following conditions: with childbearing potential: she agrees to use an effective contraceptive method or abstinence from at least 4 weeks prior to the study intervention administration until at least 12 weeks after the study intervention administration, or with non-childbearing potential. to be considered of non-childbearing potential, a female must be post-menopausal for at least 1 year or surgically sterile participants must be in general good health* based on medical history and physical examination, as determined by the pi at screening. participants must agree to refrain from donating blood, plasma, ova, sperm, or organs during the whole study.