inclusion criteria: * had given informed consent by signing the informed consent form (icf) before initiation of any trial-specific procedures. * volunteers who at the time of consent were: * part a: 18 to 55 years old. * part b and part c: 18 to 85 years old (\~60% should be 18 to 55 years old and \~40% 56 to 85 years old). * for cohorts 1 to 5: in part a, who had received bnt162b2 vaccine (30 µg, two-dose regimen) in either a clinical trial or as part of the governmental vaccination programs at least 6 months before visit 0. participants who were currently enrolled in the phase iii bnt162-02 / c4591001 (nct04368728) trial, had already been unblinded, and had previously received two doses of bnt162b2 at least 6 months earlier could be included (for cohorts 1 and 4 in part b, prior enrollment and dosing in the c4591001 trial was mandatory). at enrollment into part b of this trial, their participation in the c4591001 trial was terminated. participants should have not had experienced covid-19 based on medical history. * for cohort 6: were covid-19 vaccine-naïve and had not experienced covid-19 based on their medical history. * were willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other trial procedures. * were overall healthy at visit 0 in the clinical judgment of the investigator based on the medical history, clinical assessment (including physical examination, vital signs, blood and urine clinical laboratory tests, 12-lead electrocardiogram (ecg), and oral swab for nucleic acid amplification-based test (naat)-based severe acute respiratory syndrome coronavirus 2 (sars-cov-2) testing). * note: healthy volunteers with pre-existing stable disease, defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 12 weeks before visit 0, could be included. * note: volunteers who had hepatitis c (hcv) infection, but had completed curative treatment based on the medical history could be included. volunteers who had or have hepatitis b (hbv) or human immunodeficiency virus (hiv) based on the medical history could not be included. * agreed not to enroll in another trial of an investigational medicinal product (imp), starting after visit 0 and continuously until the last planned visit in this trial. * women of childbearing potential (wocbp) had to test negative in a urine beta-human chorionic gonadotropin (β-hcg) test at visits 0 and 1. * wocbp had to agree to practice a highly effective form of contraception starting at visit 0 and continuously until 28 days after their last imp administration in this trial. * wocbp had to confirm that they practiced an acceptable form of contraception for the 14 days prior to visit 0. * wocbp had to agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction starting after visit 0 and continuously until 28 days after their last imp injection in this trial. * men who are sexually active with a wocbp and had not had a vasectomy had to agree to use a highly effective form of contraception with their female partner of childbearing potential starting after visit 0 and continuously until 28 days after their last imp injection in this trial. * men had to be willing to refrain from sperm donation, starting after visit 0 and continuously until 28 days after their last vaccination. * for part c, cohorts 7, 8, and 9: had received two or three documented doses of any authorized covid-19 rna-based vaccine (e.g., bnt162b2 \[comirnaty\] or the moderna vaccine \[spikevax\]) prior to being diagnosed with sars-cov-2 infection from january 2022 onwards (and limited to a period when there was a high prevalence of sars-cov-2 omicron infections). * note: the interval between the last covid-19 rna-based vaccine administered and randomization should have been \>4 months. the latest prior diagnosed sars-cov-2 infection should have been at least 2 months before randomization. the latest sars-cov-2 infection should have been documented with a result from a naat (as a preferable option). in case no historic naat result was available proving prior sars-cov-2 infection, the local positive result of sars-cov-2 n-binding antibodies done at screening was sufficient.

inclusion criteria: * had given informed consent by signing the informed consent form (icf) before initiation of any trial-specific procedures. * volunteers who at the time of consent were: * part a: 18 to 55 years old. * part b and part c: 18 to 85 years old (\~60% should be 18 to 55 years old and \~40% 56 to 85 years old). * for cohorts 1 to 5: in part a, who had received bnt162b2 vaccine (30 µg, two-dose regimen) in either a clinical trial or as part of the governmental vaccination programs at least 6 months before visit 0. participants who were currently enrolled in the phase iii bnt162-02 / c4591001 (nct04368728) trial, had already been unblinded, and had previously received two doses of bnt162b2 at least 6 months earlier could be included (for cohorts 1 and 4 in part b, prior enrollment and dosing in the c4591001 trial was mandatory). at enrollment into part b of this trial, their participation in the c4591001 trial was terminated. participants should have not had experienced covid-19 based on medical history. * for cohort 6: were covid-19 vaccine-naïve and had not experienced covid-19 based on their medical history. * were willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other trial procedures. * were overall healthy at visit 0 in the clinical judgment of the investigator based on the medical history, clinical assessment (including physical examination, vital signs, blood and urine clinical laboratory tests, 12-lead electrocardiogram (ecg), and oral swab for nucleic acid amplification-based test (naat)-based severe acute respiratory syndrome coronavirus 2 (sars-cov-2) testing). * note: healthy volunteers with pre-existing stable disease, defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 12 weeks before visit 0, could be included. * note: volunteers who had hepatitis c (hcv) infection, but had completed curative treatment based on the medical history could be included. volunteers who had or have hepatitis b (hbv) or human immunodeficiency virus (hiv) based on the medical history could not be included. * agreed not to enroll in another trial of an investigational medicinal product (imp), starting after visit 0 and continuously until the last planned visit in this trial. * women of childbearing potential (wocbp) had to test negative in a urine beta-human chorionic gonadotropin (β-hcg) test at visits 0 and 1. * wocbp had to agree to practice a highly effective form of contraception starting at visit 0 and continuously until 28 days after their last imp administration in this trial. * wocbp had to confirm that they practiced an acceptable form of contraception for the 14 days prior to visit 0. * wocbp had to agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction starting after visit 0 and continuously until 28 days after their last imp injection in this trial. * men who are sexually active with a wocbp and had not had a vasectomy had to agree to use a highly effective form of contraception with their female partner of childbearing potential starting after visit 0 and continuously until 28 days after their last imp injection in this trial. * men had to be willing to refrain from sperm donation, starting after visit 0 and continuously until 28 days after their last vaccination. * for part c, cohorts 7, 8, and 9: had received two or three documented doses of any authorized covid-19 rna-based vaccine (e.g., bnt162b2 \[comirnaty\] or the moderna vaccine \[spikevax\]) prior to being diagnosed with sars-cov-2 infection from january 2022 onwards (and limited to a period when there was a high prevalence of sars-cov-2 omicron infections). * note: the interval between the last covid-19 rna-based vaccine administered and randomization should have been \>4 months. the latest prior diagnosed sars-cov-2 infection should have been at least 2 months before randomization. the latest sars-cov-2 infection should have been documented with a result from a naat (as a preferable option). in case no historic naat result was available proving prior sars-cov-2 infection, the local positive result of sars-cov-2 n-binding antibodies done at screening was sufficient.

inclusion criteria: * have given informed consent by signing the informed consent form (icf) before initiation of any trial-specific procedures. * volunteers who at the time of consent are: * part a: 18 to 55 years old. * part b and part c: 18 to 85 years old (\~60% should be 18 to 55 years old and \~40% 56 to 85 years old). * for cohorts 1 to 5: in part a, who have received bnt162b2 vaccine (30 µg, two-dose regimen) in either a clinical trial or as part of the governmental vaccination programs at least 6 months before visit 0. participants who are currently enrolled in the phase iii bnt162-02 / c4591001 trial, have already been unblinded, and have previously received two doses of bnt162b2 at least 6 months earlier can be included (for cohorts 1 and 4 in part b, prior enrollment and dosing in the bnt162-02 / c4591001 trial is mandatory). at enrollment into part b of this trial, their participation in the bnt162-02 / c4591001 trial will be terminated. participants should have not experienced covid-19 based on medical history. * for cohort 6: are covid-19 vaccine-naïve and have not experienced covid-19 based on their medical history. * are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other trial procedures. * are overall healthy at visit 0 in the clinical judgment of the investigator based on the medical history, clinical assessment (including physical examination, vital signs, blood and urine clinical laboratory tests, 12-lead electrocardiogram (ecg), and oral swab for nucleic acid amplification-based test (naat)-based severe acute respiratory syndrome coronavirus 2 (sars-cov-2) testing). * note: healthy volunteers with pre-existing stable disease, defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 12 weeks before visit 0, can be included. * note: volunteers who had hepatitis c (hcv) infection, but have completed curative treatment based on the medical history can be included. volunteers who had or have hepatitis b (hbv) or human immunodeficiency virus (hiv) based on the medical history cannot be included. * agree not to enroll in another trial of an investigational medicinal product (imp), starting after visit 0 and continuously until the last planned visit in this trial. * women of childbearing potential (wocbp) must test negative in a urine beta-human chorionic gonadotropin (β-hcg) test at visits 0 and 1. * wocbp must agree to practice a highly effective form of contraception starting at visit 0 and continuously until 28 days after their last imp administration in this trial. * wocbp must confirm that they practiced an acceptable form of contraception for the 14 days prior to visit 0. * wocbp must agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction starting after visit 0 and continuously until 28 days after their last imp injection in this trial. * men who are sexually active with a wocbp and have not had a vasectomy must agree to use a highly effective form of contraception with their female partner of childbearing potential starting after visit 0 and continuously until 28 days after their last imp injection in this trial. * men must be willing to refrain from sperm donation, starting after visit 0 and continuously until 28 days after their last vaccination. * for part c, cohorts 7, 8, and 9: have received two or three documented doses of any authorized covid-19 rna-based vaccine (e.g., bnt162b2 \[comirnaty\] or the moderna vaccine \[spikevax\]) prior to being diagnosed with sars-cov-2 infection from january 2022 onwards (and limited to a period when there was a high prevalence of sars-cov-2 omicron infections). * note: the interval between the last covid-19 rna-based vaccine administered and randomization should be \>4 months. the latest prior diagnosed sars-cov-2 infection should be at least 2 months before randomization. the latest sars-cov-2 infection should be documented with a result from a naat (as a preferable option). in case no historic naat result is available proving prior sars-cov-2 infection, the local positive result of sars-cov-2 n-binding antibodies done at screening will be sufficient.

inclusion criteria: * have given informed consent by signing the informed consent form (icf) before initiation of any trial-specific procedures. * volunteers who at the time of consent are: * part a: 18 to 55 years old. * part b and part c: 18 to 85 years old (\~60% should be 18 to 55 years old and \~40% 56 to 85 years old). * for cohorts 1 to 5: in part a, who have received bnt162b2 vaccine (30 µg, two-dose regimen) in either a clinical trial or as part of the governmental vaccination programs at least 6 months before visit 0. participants who are currently enrolled in the phase iii bnt162-02 / c4591001 trial, have already been unblinded, and have previously received two doses of bnt162b2 at least 6 months earlier can be included (for cohorts 1 and 4 in part b, prior enrollment and dosing in the bnt162-02 / c4591001 trial is mandatory). at enrollment into part b of this trial, their participation in the bnt162-02 / c4591001 trial will be terminated. participants should have not experienced covid-19 based on medical history. * for cohort 6: are covid-19 vaccine-naïve and have not experienced covid-19 based on their medical history. * are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other trial procedures. * are overall healthy at visit 0 in the clinical judgment of the investigator based on the medical history, clinical assessment (including physical examination, vital signs, blood and urine clinical laboratory tests, 12-lead electrocardiogram (ecg), and oral swab for nucleic acid amplification-based test (naat)-based severe acute respiratory syndrome coronavirus 2 (sars-cov-2) testing). * note: healthy volunteers with pre-existing stable disease, defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 12 weeks before visit 0, can be included. * note: volunteers who had hepatitis c (hcv) infection, but have completed curative treatment based on the medical history can be included. volunteers who had or have hepatitis b (hbv) or human immunodeficiency virus (hiv) based on the medical history cannot be included. * agree not to enroll in another trial of an investigational medicinal product (imp), starting after visit 0 and continuously until the last planned visit in this trial. * women of childbearing potential (wocbp) must test negative in a urine beta-human chorionic gonadotropin (β-hcg) test at visits 0 and 1. * wocbp must agree to practice a highly effective form of contraception starting at visit 0 and continuously until 28 days after their last imp administration in this trial. * wocbp must confirm that they practiced an acceptable form of contraception for the 14 days prior to visit 0. * wocbp must agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction starting after visit 0 and continuously until 28 days after their last imp injection in this trial. * men who are sexually active with a wocbp and have not had a vasectomy must agree to use a highly effective form of contraception with their female partner of childbearing potential starting after visit 0 and continuously until 28 days after their last imp injection in this trial. * men must be willing to refrain from sperm donation, starting after visit 0 and continuously until 28 days after their last vaccination. * for part c, cohorts 7, 8, and 9: have received two or three documented doses of any authorized covid-19 rna-based vaccine (e.g., bnt162b2 \[comirnaty\] or the moderna vaccine \[spikevax\]) prior to being diagnosed with sars-cov-2 infection from january 2022 onwards (and limited to a period when there was a high prevalence of sars-cov-2 omicron infections). * note: the interval between the last covid-19 rna-based vaccine administered and randomization should be \>4 months. the latest prior diagnosed sars-cov-2 infection should be at least 2 months before randomization. the latest sars-cov-2 infection should be documented with a result from a naat (as a preferable option). in case no historic naat result is available proving prior sars-cov-2 infection, the local positive result of sars-cov-2 n-binding antibodies done at screening will be sufficient.

inclusion criteria: have given informed consent by signing the informed consent form (icf) before initiation of any trial-specific procedures. volunteers who at the time of consent are: part a: 18 to 55 years old. part b and part c: 18 to 85 years old (~60% should be 18 to 55 years old and ~40% 56 to 85 years old). for cohorts 1 to 5: in part a, who have received bnt162b2 vaccine (30 µg, two-dose regimen) in either a clinical trial or as part of the governmental vaccination programs at least 6 months before visit 0. participants who are currently enrolled in the phase iii bnt162-02 / c4591001 trial, have already been unblinded, and have previously received two doses of bnt162b2 at least 6 months earlier can be included (for cohorts 1 and 4 in part b, prior enrollment and dosing in the bnt162-02 / c4591001 trial is mandatory). at enrollment into part b of this trial, their participation in the bnt162-02 / c4591001 trial will be terminated. participants should have not experienced covid-19 based on medical history. for cohort 6: are covid-19 vaccine-naïve and have not experienced covid-19 based on their medical history. are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other trial procedures. are overall healthy at visit 0 in the clinical judgment of the investigator based on the medical history, clinical assessment (including physical examination, vital signs, blood and urine clinical laboratory tests, 12-lead electrocardiogram (ecg), and oral swab for nucleic acid amplification-based test (naat)-based severe acute respiratory syndrome coronavirus 2 (sars-cov-2) testing). note: healthy volunteers with pre-existing stable disease, defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 12 weeks before visit 0, can be included. note: volunteers who had hepatitis c (hcv) infection, but have completed curative treatment based on the medical history can be included. volunteers who had or have hepatitis b (hbv) or human immunodeficiency virus (hiv) based on the medical history cannot be included. agree not to enroll in another trial of an investigational medicinal product (imp), starting after visit 0 and continuously until the last planned visit in this trial. women of childbearing potential (wocbp) must test negative in a urine beta-human chorionic gonadotropin (β-hcg) test at visits 0 and 1. wocbp must agree to practice a highly effective form of contraception starting at visit 0 and continuously until 28 days after their last imp administration in this trial. wocbp must confirm that they practiced an acceptable form of contraception for the 14 days prior to visit 0. wocbp must agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction starting after visit 0 and continuously until 28 days after their last imp injection in this trial. men who are sexually active with a wocbp and have not had a vasectomy must agree to use a highly effective form of contraception with their female partner of childbearing potential starting after visit 0 and continuously until 28 days after their last imp injection in this trial. men must be willing to refrain from sperm donation, starting after visit 0 and continuously until 28 days after their last vaccination. for part c, cohorts 7, 8, and 9: have received two or three documented doses of any authorized covid-19 rna-based vaccine (e.g., bnt162b2 [comirnaty] or the moderna vaccine [spikevax]) prior to being diagnosed with sars-cov-2 infection from january 2022 onwards (and limited to a period when there was a high prevalence of sars-cov-2 omicron infections). note: the interval between the last covid-19 rna-based vaccine administered and randomization should be >4 months. the latest prior diagnosed sars-cov-2 infection should be at least 2 months before randomization. the latest sars-cov-2 infection should be documented with a result from a naat (as a preferable option). in case no historic naat result is available proving prior sars-cov-2 infection, the local positive result of sars-cov-2 n-binding antibodies done at screening will be sufficient.

inclusion criteria: have given informed consent by signing the informed consent form (icf) before initiation of any trial-specific procedures. volunteers who at the time of consent are: part a: 18 to 55 years old. part b and part c: 18 to 85 years old (~60% should be 18 to 55 years old and ~40% 56 to 85 years old). for cohorts 1 to 5: in part a, who have received bnt162b2 vaccine (30 µg, two-dose regimen) in either a clinical trial or as part of the governmental vaccination programs at least 6 months before visit 0. participants who are currently enrolled in the phase iii bnt162-02 / c4591001 trial, have already been unblinded, and have previously received two doses of bnt162b2 at least 6 months earlier can be included (for cohorts 1 and 4 in part b, prior enrollment and dosing in the bnt162-02 / c4591001 trial is mandatory). at enrollment into part b of this trial, their participation in the bnt162-02 / c4591001 trial will be terminated. participants should have not experienced covid-19 based on medical history. for cohort 6: are covid-19 vaccine-naïve and have not experienced covid-19 based on their medical history. are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other trial procedures. are overall healthy at visit 0 in the clinical judgment of the investigator based on the medical history, clinical assessment (including physical examination, vital signs, blood and urine clinical laboratory tests, 12-lead electrocardiogram (ecg), and oral swab for nucleic acid amplification-based test (naat)-based severe acute respiratory syndrome coronavirus 2 (sars-cov-2) testing). note: healthy volunteers with pre-existing stable disease, defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 12 weeks before visit 0, can be included. note: volunteers who had hepatitis c (hcv) infection, but have completed curative treatment based on the medical history can be included. volunteers who had or have hepatitis b (hbv) or human immunodeficiency virus (hiv) based on the medical history cannot be included. agree not to enroll in another trial of an investigational medicinal product (imp), starting after visit 0 and continuously until the last planned visit in this trial. women of childbearing potential (wocbp) must test negative in a urine beta-human chorionic gonadotropin (β-hcg) test at visits 0 and 1. wocbp must agree to practice a highly effective form of contraception starting at visit 0 and continuously until 28 days after their last imp administration in this trial. wocbp must confirm that they practiced an acceptable form of contraception for the 14 days prior to visit 0. wocbp must agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction starting after visit 0 and continuously until 28 days after their last imp injection in this trial. men who are sexually active with a wocbp and have not had a vasectomy must agree to use a highly effective form of contraception with their female partner of childbearing potential starting after visit 0 and continuously until 28 days after their last imp injection in this trial. men must be willing to refrain from sperm donation, starting after visit 0 and continuously until 28 days after their last vaccination. for part c, cohorts 7, 8, and 9: have received two or three documented doses of any authorized covid-19 rna-based vaccine (e.g., bnt162b2 [comirnaty] or the moderna vaccine [spikevax]) prior to being diagnosed with sars-cov-2 infection from january 2022 onwards (and limited to a period when there was a high prevalence of sars-cov-2 omicron infections). note: the interval between the last covid-19 rna-based vaccine administered and randomization should be >4 months. the latest prior diagnosed sars-cov-2 infection should be at least 2 months before randomization. the latest sars-cov-2 infection should be documented with a result from a naat (as a preferable option). in case no historic naat result is available proving prior sars-cov-2 infection, the local positive result of sars-cov-2 n-binding antibodies done at screening will be sufficient.

inclusion criteria: have given informed consent by signing the informed consent form (icf) before initiation of any trial-specific procedures. volunteers who at the time of consent are: part a: 18 to 55 years old. part b and part c: 18 to 85 years old (~60% should be 18 to 55 years old and ~40% 56 to 85 years old). for cohorts 1 to 5: in part a, who have received bnt162b2 vaccine (30 µg, two-dose regimen) in either a clinical trial or as part of the governmental vaccination programs at least 6 months before visit 0. participants who are currently enrolled in the phase iii bnt162-02 / c4591001 trial, have already been unblinded, and have previously received two doses of bnt162b2 at least 6 months earlier can be included (for cohorts 1 and 4 in part b, prior enrollment and dosing in the bnt162-02 / c4591001 trial is mandatory). at enrollment into part b of this trial, their participation in the bnt162-02 / c4591001 trial will be terminated. participants should have not experienced covid-19 based on medical history. for cohort 6: are covid-19 vaccine-naïve and have not experienced covid-19 based on their medical history. are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other trial procedures. are overall healthy at visit 0 in the clinical judgment of the investigator based on the medical history, clinical assessment (including physical examination, vital signs, blood and urine clinical laboratory tests, 12-lead electrocardiogram (ecg), and oral swab for nucleic acid amplification-based test (naat)-based severe acute respiratory syndrome coronavirus 2 (sars-cov-2) testing). note: healthy volunteers with pre-existing stable disease, defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 12 weeks before visit 0, can be included. note: volunteers who had hepatitis c (hcv) infection, but have completed curative treatment based on the medical history can be included. volunteers who had or have hepatitis b (hbv) or human immunodeficiency virus (hiv) based on the medical history cannot be included. agree not to enroll in another trial of an investigational medicinal product (imp), starting after visit 0 and continuously until the last planned visit in this trial. women of childbearing potential (wocbp) must test negative in a urine beta-human chorionic gonadotropin (β-hcg) test at visits 0 and 1. wocbp must agree to practice a highly effective form of contraception starting at visit 0 and continuously until 28 days after their last imp administration in this trial. wocbp must confirm that they practiced an acceptable form of contraception for the 14 days prior to visit 0. wocbp must agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction starting after visit 0 and continuously until 28 days after their last imp injection in this trial. men who are sexually active with a wocbp and have not had a vasectomy must agree to use a highly effective form of contraception with their female partner of childbearing potential starting after visit 0 and continuously until 28 days after their last imp injection in this trial. men must be willing to refrain from sperm donation, starting after visit 0 and continuously until 28 days after their last vaccination. for part c, cohorts 7, 8, and 9: have received two or three documented doses of any authorized covid-19 rna-based vaccine (e.g., bnt162b2 [comirnaty] or the moderna vaccine [spikevax]) prior to being diagnosed with sars-cov-2 infection from january 2022 on (and limited to a period when there was a high prevalence of sars-cov-2 omicron infections) that is documented with a result from a nucleic acid amplification-based test (naat) for sars-cov-2.

inclusion criteria: have given informed consent by signing the informed consent form (icf) before initiation of any trial-specific procedures. volunteers who at the time of consent are: part a: 18 to 55 years old. part b and part c: 18 to 85 years old (~60% should be 18 to 55 years old and ~40% 56 to 85 years old). for cohorts 1 to 5: in part a, who have received bnt162b2 vaccine (30 µg, two-dose regimen) in either a clinical trial or as part of the governmental vaccination programs at least 6 months before visit 0. participants who are currently enrolled in the phase iii bnt162-02 / c4591001 trial, have already been unblinded, and have previously received two doses of bnt162b2 at least 6 months earlier can be included (for cohorts 1 and 4 in part b, prior enrollment and dosing in the bnt162-02 / c4591001 trial is mandatory). at enrollment into part b of this trial, their participation in the bnt162-02 / c4591001 trial will be terminated. participants should have not experienced covid-19 based on medical history. for cohort 6: are covid-19 vaccine-naïve and have not experienced covid-19 based on their medical history. are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other trial procedures. are overall healthy at visit 0 in the clinical judgment of the investigator based on the medical history, clinical assessment (including physical examination, vital signs, blood and urine clinical laboratory tests, 12-lead electrocardiogram (ecg), and oral swab for nucleic acid amplification-based test (naat)-based severe acute respiratory syndrome coronavirus 2 (sars-cov-2) testing). note: healthy volunteers with pre-existing stable disease, defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 12 weeks before visit 0, can be included. note: volunteers who had hepatitis c (hcv) infection, but have completed curative treatment based on the medical history can be included. volunteers who had or have hepatitis b (hbv) or human immunodeficiency virus (hiv) based on the medical history cannot be included. agree not to enroll in another trial of an investigational medicinal product (imp), starting after visit 0 and continuously until the last planned visit in this trial. women of childbearing potential (wocbp) must test negative in a urine beta-human chorionic gonadotropin (β-hcg) test at visits 0 and 1. wocbp must agree to practice a highly effective form of contraception starting at visit 0 and continuously until 28 days after their last imp administration in this trial. wocbp must confirm that they practiced an acceptable form of contraception for the 14 days prior to visit 0. wocbp must agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction starting after visit 0 and continuously until 28 days after their last imp injection in this trial. men who are sexually active with a wocbp and have not had a vasectomy must agree to use a highly effective form of contraception with their female partner of childbearing potential starting after visit 0 and continuously until 28 days after their last imp injection in this trial. men must be willing to refrain from sperm donation, starting after visit 0 and continuously until 28 days after their last vaccination. for part c, cohorts 7, 8, and 9: have received two or three documented doses of any authorized covid-19 rna-based vaccine (e.g., bnt162b2 [comirnaty] or the moderna vaccine [spikevax]) prior to being diagnosed with sars-cov-2 infection from january 2022 on (and limited to a period when there was a high prevalence of sars-cov-2 omicron infections) that is documented with a result from a nucleic acid amplification-based test (naat) for sars-cov-2.

inclusion criteria: - have given informed consent by signing the informed consent form (icf) before initiation of any trial-specific procedures. - volunteers who at the time of consent are: - part a: 18 to 55 years old. - part b: 18 to 85 years old (~60% should be 18 to 55 years old and ~40% 56 to 85 years old). - for cohorts 1 to 5: have received bnt162b2 vaccine (30 µg, two-dose regimen) in either a clinical trial or as part of the governmental vaccination programs at least 6 months before visit 0. participants who are currently enrolled in the phase iii bnt162-02 / c4591001 trial, have already been unblinded, and have previously received two doses of bnt162b2 at least 6 months earlier can be included. at enrollment into part b of this trial, their participation in the bnt162-02 / c4591001 trial will be terminated. participants should have not experienced covid-19 based on medical history. - for cohort 6: are covid-19 vaccine-naïve and have not experienced covid-19 based on their medical history. - are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other trial procedures. - are overall healthy at visit 0 in the clinical judgment of the investigator based on the medical history, clinical assessment (including physical examination, vital signs, blood and urine clinical laboratory tests, 12-lead electrocardiogram (ecg), and oral swab for nucleic acid amplification-based test (naat)-based severe acute respiratory syndrome coronavirus 2 (sars-cov-2) testing). note: healthy volunteers with pre-existing stable disease, defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 12 weeks before visit 0, can be included. note: volunteers who had hepatitis c (hcv) infection, but have completed curative treatment based on the medical history can be included. volunteers who had or have hepatitis b (hbv) or human immunodeficiency virus (hiv) based on the medical history cannot be included. - agree not to enroll in another trial of an investigational medicinal product (imp), starting after visit 0 and continuously until the last planned visit in this trial. - women of childbearing potential (wocbp) must test negative in a urine beta-human chorionic gonadotropin (β-hcg) test at visits 0 and 1. - wocbp must agree to practice a highly effective form of contraception starting at visit 0 and continuously until 28 days after their last imp administration in this trial. - wocbp must confirm that they practiced an acceptable form of contraception for the 14 days prior to visit 0. - wocbp must agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction starting after visit 0 and continuously until 28 days after their last imp injection in this trial. - men who are sexually active with a wocbp and have not had a vasectomy must agree to use a highly effective form of contraception with their female partner of childbearing potential starting after visit 0 and continuously until 28 days after their last imp injection in this trial. - men must be willing to refrain from sperm donation, starting after visit 0 and continuously until 28 days after their last vaccination.

inclusion criteria: - have given informed consent by signing the informed consent form (icf) before initiation of any trial-specific procedures. - volunteers who at the time of consent are: - part a: 18 to 55 years old. - part b: 18 to 85 years old (~60% should be 18 to 55 years old and ~40% 56 to 85 years old). - for cohorts 1 to 5: have received bnt162b2 vaccine (30 µg, two-dose regimen) in either a clinical trial or as part of the governmental vaccination programs at least 6 months before visit 0. participants who are currently enrolled in the phase iii bnt162-02 / c4591001 trial, have already been unblinded, and have previously received two doses of bnt162b2 at least 6 months earlier can be included. at enrollment into part b of this trial, their participation in the bnt162-02 / c4591001 trial will be terminated. participants should have not experienced covid-19 based on medical history. - for cohort 6: are covid-19 vaccine-naïve and have not experienced covid-19 based on their medical history. - are willing and able to comply with all scheduled visits, vaccination plan, laboratory tests, lifestyle considerations, and other trial procedures. - are overall healthy at visit 0 in the clinical judgment of the investigator based on the medical history, clinical assessment (including physical examination, vital signs, blood and urine clinical laboratory tests, 12-lead electrocardiogram (ecg), and oral swab for nucleic acid amplification-based test (naat)-based severe acute respiratory syndrome coronavirus 2 (sars-cov-2) testing). note: healthy volunteers with pre-existing stable disease, defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 12 weeks before visit 0, can be included. note: volunteers who had hepatitis c (hcv) infection, but have completed curative treatment based on the medical history can be included. volunteers who had or have hepatitis b (hbv) or human immunodeficiency virus (hiv) based on the medical history cannot be included. - agree not to enroll in another trial of an investigational medicinal product (imp), starting after visit 0 and continuously until the last planned visit in this trial. - women of childbearing potential (wocbp) must test negative in a urine beta-human chorionic gonadotropin (β-hcg) test at visits 0 and 1. - wocbp must agree to practice a highly effective form of contraception starting at visit 0 and continuously until 28 days after their last imp administration in this trial. - wocbp must confirm that they practiced an acceptable form of contraception for the 14 days prior to visit 0. - wocbp must agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction starting after visit 0 and continuously until 28 days after their last imp injection in this trial. - men who are sexually active with a wocbp and have not had a vasectomy must agree to use a highly effective form of contraception with their female partner of childbearing potential starting after visit 0 and continuously until 28 days after their last imp injection in this trial. - men must be willing to refrain from sperm donation, starting after visit 0 and continuously until 28 days after their last vaccination.