inclusion criteria: * groups 1, 2 and 3 only: healthy adults aged 18-55 years (note, prior to implementation of sa001, a single participant under the age of 30 was enrolled in group 1a. this participant will be retained for follow-up but will not receive a booster vaccine, in light of the new age restrictions. between the implementation of sa001 and implementation of sa003, only those aged 30-40 years were eligible. * groups 4 and 5 only: healthy adults aged 30-55 years * able and willing (in the investigator's opinion) to comply with all study requirements * willing to allow the investigators to discuss the volunteer's medical history with their general practitioner and access all medical records when relevant to study procedures. * for females only, willingness to practice continuous effective contraception during the study and a negative pregnancy test on the day(s) of screening and vaccination. * agreement to refrain from blood donation during the course of the study. * provide written informed consent. * group 4 only: prior receipt of 2 doses of chadox1 ncov-19 intramuscularly, with an interval of at least 8 weeks between the intramuscular doses, and with the second dose a minimum of 12 weeks prior to enrolment * group 5 only: prior receipt of 2 doses of bnt162b2 intramuscularly, with an interval of at least 3 weeks between the intramuscular doses, and with the second dose a minimum of 12 weeks prior to enrolment acceptable forms of contraception for female volunteers include: * established use of oral, injected or implanted hormonal methods of contraception. * placement of an intrauterine device (iud) or intrauterine system (ius). * total abdominal hysterectomy. * bilateral tubal occlusion barrier methods of contraception (condom or occlusive cap with spermicide). * male sterilisation, if the vasectomised partner is the sole partner for the subject. * true abstinence, when this is in line with the preferred and usual lifestyle of the subject. * periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods), declaration of abstinence for the duration of exposure to imp, and withdrawal are not acceptable methods of contraception

inclusion criteria: * groups 1, 2 and 3 only: healthy adults aged 18-55 years (note, prior to implementation of sa001, a single participant under the age of 30 was enrolled in group 1a. this participant will be retained for follow-up but will not receive a booster vaccine, in light of the new age restrictions. between the implementation of sa001 and implementation of sa003, only those aged 30-40 years were eligible. * groups 4 and 5 only: healthy adults aged 30-55 years * able and willing (in the investigator's opinion) to comply with all study requirements * willing to allow the investigators to discuss the volunteer's medical history with their general practitioner and access all medical records when relevant to study procedures. * for females only, willingness to practice continuous effective contraception during the study and a negative pregnancy test on the day(s) of screening and vaccination. * agreement to refrain from blood donation during the course of the study. * provide written informed consent. * group 4 only: prior receipt of 2 doses of chadox1 ncov-19 intramuscularly, with an interval of at least 8 weeks between the intramuscular doses, and with the second dose a minimum of 12 weeks prior to enrolment * group 5 only: prior receipt of 2 doses of bnt162b2 intramuscularly, with an interval of at least 3 weeks between the intramuscular doses, and with the second dose a minimum of 12 weeks prior to enrolment acceptable forms of contraception for female volunteers include: * established use of oral, injected or implanted hormonal methods of contraception. * placement of an intrauterine device (iud) or intrauterine system (ius). * total abdominal hysterectomy. * bilateral tubal occlusion barrier methods of contraception (condom or occlusive cap with spermicide). * male sterilisation, if the vasectomised partner is the sole partner for the subject. * true abstinence, when this is in line with the preferred and usual lifestyle of the subject. * periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods), declaration of abstinence for the duration of exposure to imp, and withdrawal are not acceptable methods of contraception

inclusion criteria: - groups 1, 2 and 3 only: healthy adults aged 18-55 years (note, prior to implementation of sa001, a single participant under the age of 30 was enrolled in group 1a. this participant will be retained for follow-up but will not receive a booster vaccine, in light of the new age restrictions. between the implementation of sa001 and implementation of sa003, only those aged 30-40 years were eligible. - groups 4 and 5 only: healthy adults aged 30-55 years - able and willing (in the investigator's opinion) to comply with all study requirements - willing to allow the investigators to discuss the volunteer's medical history with their general practitioner and access all medical records when relevant to study procedures. - for females only, willingness to practice continuous effective contraception during the study and a negative pregnancy test on the day(s) of screening and vaccination. - agreement to refrain from blood donation during the course of the study. - provide written informed consent. - group 4 only: prior receipt of 2 doses of chadox1 ncov-19 intramuscularly, with an interval of at least 8 weeks between the intramuscular doses, and with the second dose a minimum of 12 weeks prior to enrolment - group 5 only: prior receipt of 2 doses of bnt162b2 intramuscularly, with an interval of at least 3 weeks between the intramuscular doses, and with the second dose a minimum of 12 weeks prior to enrolment acceptable forms of contraception for female volunteers include: - established use of oral, injected or implanted hormonal methods of contraception. - placement of an intrauterine device (iud) or intrauterine system (ius). - total abdominal hysterectomy. - bilateral tubal occlusion barrier methods of contraception (condom or occlusive cap with spermicide). - male sterilisation, if the vasectomised partner is the sole partner for the subject. - true abstinence, when this is in line with the preferred and usual lifestyle of the subject. - periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods), declaration of abstinence for the duration of exposure to imp, and withdrawal are not acceptable methods of contraception

inclusion criteria: - groups 1, 2 and 3 only: healthy adults aged 18-55 years (note, prior to implementation of sa001, a single participant under the age of 30 was enrolled in group 1a. this participant will be retained for follow-up but will not receive a booster vaccine, in light of the new age restrictions. between the implementation of sa001 and implementation of sa003, only those aged 30-40 years were eligible. - groups 4 and 5 only: healthy adults aged 30-55 years - able and willing (in the investigator's opinion) to comply with all study requirements - willing to allow the investigators to discuss the volunteer's medical history with their general practitioner and access all medical records when relevant to study procedures. - for females only, willingness to practice continuous effective contraception during the study and a negative pregnancy test on the day(s) of screening and vaccination. - agreement to refrain from blood donation during the course of the study. - provide written informed consent. - group 4 only: prior receipt of 2 doses of chadox1 ncov-19 intramuscularly, with an interval of at least 8 weeks between the intramuscular doses, and with the second dose a minimum of 12 weeks prior to enrolment - group 5 only: prior receipt of 2 doses of bnt162b2 intramuscularly, with an interval of at least 3 weeks between the intramuscular doses, and with the second dose a minimum of 12 weeks prior to enrolment acceptable forms of contraception for female volunteers include: - established use of oral, injected or implanted hormonal methods of contraception. - placement of an intrauterine device (iud) or intrauterine system (ius). - total abdominal hysterectomy. - bilateral tubal occlusion barrier methods of contraception (condom or occlusive cap with spermicide). - male sterilisation, if the vasectomised partner is the sole partner for the subject. - true abstinence, when this is in line with the preferred and usual lifestyle of the subject. - periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods), declaration of abstinence for the duration of exposure to imp, and withdrawal are not acceptable methods of contraception

inclusion criteria: - healthy adults aged 18-55 years (note, prior to implementation of sa001, a single participant under the age of 30 was enrolled in group 1a. this participant will be retained for follow-up but will not receive a booster vaccine, in light of the new age restrictions. between the implementation of sa001 and implementation of sa003, only those aged 30-40 years were eligible. - able and willing (in the investigator's opinion) to comply with all study requirements - willing to allow the investigators to discuss the volunteer's medical history with their general practitioner and access all medical records when relevant to study procedures. - for females only, willingness to practice continuous effective contraception during the study and a negative pregnancy test on the day(s) of screening and vaccination. - agreement to refrain from blood donation during the course of the study. - provide written informed consent. acceptable forms of contraception for female volunteers include: - established use of oral, injected or implanted hormonal methods of contraception. - placement of an intrauterine device (iud) or intrauterine system (ius). - total abdominal hysterectomy. - bilateral tubal occlusion barrier methods of contraception (condom or occlusive cap with spermicide). - male sterilisation, if the vasectomised partner is the sole partner for the subject. - true abstinence, when this is in line with the preferred and usual lifestyle of the subject. - periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods), declaration of abstinence for the duration of exposure to imp, and withdrawal are not acceptable methods of contraception

inclusion criteria: - healthy adults aged 18-55 years (note, prior to implementation of sa001, a single participant under the age of 30 was enrolled in group 1a. this participant will be retained for follow-up but will not receive a booster vaccine, in light of the new age restrictions. between the implementation of sa001 and implementation of sa003, only those aged 30-40 years were eligible. - able and willing (in the investigator's opinion) to comply with all study requirements - willing to allow the investigators to discuss the volunteer's medical history with their general practitioner and access all medical records when relevant to study procedures. - for females only, willingness to practice continuous effective contraception during the study and a negative pregnancy test on the day(s) of screening and vaccination. - agreement to refrain from blood donation during the course of the study. - provide written informed consent. acceptable forms of contraception for female volunteers include: - established use of oral, injected or implanted hormonal methods of contraception. - placement of an intrauterine device (iud) or intrauterine system (ius). - total abdominal hysterectomy. - bilateral tubal occlusion barrier methods of contraception (condom or occlusive cap with spermicide). - male sterilisation, if the vasectomised partner is the sole partner for the subject. - true abstinence, when this is in line with the preferred and usual lifestyle of the subject. - periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods), declaration of abstinence for the duration of exposure to imp, and withdrawal are not acceptable methods of contraception

inclusion criteria: - healthy adults aged 30-40 years (note, volunteers enrolled before implementation of sa001 may be 18-40 years old. due to the change in eligibility criteria regarding age range, any volunteers under the age of 30 years no longer meet eligibility criteria. volunteers under the age of 30 who were enrolled before sa001 will not be withdrawn from the study. they will not receive further vaccinations but will continue with follow-up visits and procedures) - able and willing (in the investigator's opinion) to comply with all study requirements - willing to allow the investigators to discuss the volunteer's medical history with their general practitioner and access all medical records when relevant to study procedures. - for females only, willingness to practice continuous effective contraception during the study and a negative pregnancy test on the day(s) of screening and vaccination. - agreement to refrain from blood donation during the course of the study. - provide written informed consent. acceptable forms of contraception for female volunteers include: established use of oral, injected or implanted hormonal methods of contraception. placement of an intrauterine device (iud) or intrauterine system (ius). total abdominal hysterectomy. bilateral tubal occlusion barrier methods of contraception (condom or occlusive cap with spermicide). male sterilisation, if the vasectomised partner is the sole partner for the subject. true abstinence, when this is in line with the preferred and usual lifestyle of the subject. periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods), declaration of abstinence for the duration of exposure to imp, and withdrawal are not acceptable methods of contraception

inclusion criteria: - healthy adults aged 30-40 years (note, volunteers enrolled before implementation of sa001 may be 18-40 years old. due to the change in eligibility criteria regarding age range, any volunteers under the age of 30 years no longer meet eligibility criteria. volunteers under the age of 30 who were enrolled before sa001 will not be withdrawn from the study. they will not receive further vaccinations but will continue with follow-up visits and procedures) - able and willing (in the investigator's opinion) to comply with all study requirements - willing to allow the investigators to discuss the volunteer's medical history with their general practitioner and access all medical records when relevant to study procedures. - for females only, willingness to practice continuous effective contraception during the study and a negative pregnancy test on the day(s) of screening and vaccination. - agreement to refrain from blood donation during the course of the study. - provide written informed consent. acceptable forms of contraception for female volunteers include: established use of oral, injected or implanted hormonal methods of contraception. placement of an intrauterine device (iud) or intrauterine system (ius). total abdominal hysterectomy. bilateral tubal occlusion barrier methods of contraception (condom or occlusive cap with spermicide). male sterilisation, if the vasectomised partner is the sole partner for the subject. true abstinence, when this is in line with the preferred and usual lifestyle of the subject. periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods), declaration of abstinence for the duration of exposure to imp, and withdrawal are not acceptable methods of contraception

inclusion criteria: - healthy adults aged 18-40 years. - able and willing (in the investigator's opinion) to comply with all study requirements - willing to allow the investigators to discuss the volunteer's medical history with their general practitioner and access all medical records when relevant to study procedures. - for females only, willingness to practice continuous effective contraception during the study and a negative pregnancy test on the day(s) of screening and vaccination. - agreement to refrain from blood donation during the course of the study. - provide written informed consent. acceptable forms of contraception for female volunteers include: established use of oral, injected or implanted hormonal methods of contraception. placement of an intrauterine device (iud) or intrauterine system (ius). total abdominal hysterectomy. bilateral tubal occlusion barrier methods of contraception (condom or occlusive cap with spermicide). male sterilisation, if the vasectomised partner is the sole partner for the subject. true abstinence, when this is in line with the preferred and usual lifestyle of the subject. periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods), declaration of abstinence for the duration of exposure to imp, and withdrawal are not acceptable methods of contraception

inclusion criteria: - healthy adults aged 18-40 years. - able and willing (in the investigator's opinion) to comply with all study requirements - willing to allow the investigators to discuss the volunteer's medical history with their general practitioner and access all medical records when relevant to study procedures. - for females only, willingness to practice continuous effective contraception during the study and a negative pregnancy test on the day(s) of screening and vaccination. - agreement to refrain from blood donation during the course of the study. - provide written informed consent. acceptable forms of contraception for female volunteers include: established use of oral, injected or implanted hormonal methods of contraception. placement of an intrauterine device (iud) or intrauterine system (ius). total abdominal hysterectomy. bilateral tubal occlusion barrier methods of contraception (condom or occlusive cap with spermicide). male sterilisation, if the vasectomised partner is the sole partner for the subject. true abstinence, when this is in line with the preferred and usual lifestyle of the subject. periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods), declaration of abstinence for the duration of exposure to imp, and withdrawal are not acceptable methods of contraception