inclusion criteria: 1. written informed consent. 2. healthy male and female adults aged 18 - 64 at time of informed consent. 3. body mass index 18.5 - 32.0 kg/m2 and weight \> 50 kg at screening. 4. female participants: non-pregnant, non-lactating with negative pregnancy test. 5. females who agree to comply with the applicable contraceptive requirements of the protocol. 6. ≥ 6 months fully vaccinated with a (conditionally)licensed mrna vaccine against covid-19 (part b only)

inclusion criteria: 1. written informed consent. 2. healthy male and female adults aged 18 - 64 at time of informed consent. 3. body mass index 18.5 - 32.0 kg/m2 and weight \> 50 kg at screening. 4. female participants: non-pregnant, non-lactating with negative pregnancy test. 5. females who agree to comply with the applicable contraceptive requirements of the protocol. 6. ≥ 6 months fully vaccinated with a (conditionally)licensed mrna vaccine against covid-19 (part b only)

inclusion criteria: written informed consent. healthy male and female adults aged 18 - 64 at time of informed consent. body mass index 18.5 - 32.0 kg/m2 and weight > 50 kg at screening. female participants: non-pregnant, non-lactating with negative pregnancy test. females who agree to comply with the applicable contraceptive requirements of the protocol. ≥ 6 months fully vaccinated with a (conditionally)licensed mrna vaccine against covid-19 (part b only)

inclusion criteria: written informed consent. healthy male and female adults aged 18 - 64 at time of informed consent. body mass index 18.5 - 32.0 kg/m2 and weight > 50 kg at screening. female participants: non-pregnant, non-lactating with negative pregnancy test. females who agree to comply with the applicable contraceptive requirements of the protocol. ≥ 6 months fully vaccinated with a (conditionally)licensed mrna vaccine against covid-19 (part b only)

inclusion criteria: written informed consent. healthy male and female adults aged 18 - 64 at time of informed consent (phase ib only). male and female adults aged 18 and above (phase iia) at time of informed consent. phase iia: either in good or stable health in the opinion of the investigator. participants may have underlying illness as long as their symptoms are medically controlled, and they are on a stable medication for the respective underlying illness for at least 8 weeks before screening and no changes are expected dur-ing the study. body mass index 18.5 - 32.0 kg/m2 and weight > 50 kg at screening. female participants: non-pregnant, non-lactating with negative pregnancy test. females who agree to comply with the applicable contraceptive requirements of the protocol. documented previous sars-cov-2 infection (pcr-positive) or documented vaccination against sars-cov-2 with (conditionally) licensed vaccine against covid-19, at least 6 months prior to in-clusion into this study. (phase iia open-label only)

inclusion criteria: written informed consent. healthy male and female adults aged 18 - 64 at time of informed consent (phase ib only). male and female adults aged 18 and above (phase iia) at time of informed consent. phase iia: either in good or stable health in the opinion of the investigator. participants may have underlying illness as long as their symptoms are medically controlled, and they are on a stable medication for the respective underlying illness for at least 8 weeks before screening and no changes are expected dur-ing the study. body mass index 18.5 - 32.0 kg/m2 and weight > 50 kg at screening. female participants: non-pregnant, non-lactating with negative pregnancy test. females who agree to comply with the applicable contraceptive requirements of the protocol. documented previous sars-cov-2 infection (pcr-positive) or documented vaccination against sars-cov-2 with (conditionally) licensed vaccine against covid-19, at least 6 months prior to in-clusion into this study. (phase iia open-label only)

inclusion criteria: 1. written informed consent. 2. healthy male and female adults aged 18 - 64 at time of informed consent (phase ib only). 3. male and female adults aged 18 and above (phase iia) at time of informed consent. 4. phase iia: either in good or stable health in the opinion of the investigator. participants may have underlying illness as long as their symptoms are medically controlled, and they are on a stable medication for the respective underlying illness for at least 8 weeks before screening and no changes are expected dur-ing the study. 5. body mass index 18.5 - 32.0 kg/m2 and weight > 50 kg at screening. 6. female participants: non-pregnant, non-lactating with negative pregnancy test. 7. females who agree to comply with the applicable contraceptive requirements of the protocol. 8. documented previous sars-cov-2 infection (pcr-positive) or documented vaccination against sars-cov-2 with (conditionally) licensed vaccine against covid-19, at least 6 months prior to in-clusion into this study. (phase iia open-label only)

inclusion criteria: 1. written informed consent. 2. healthy male and female adults aged 18 - 64 at time of informed consent (phase ib only). 3. male and female adults aged 18 and above (phase iia) at time of informed consent. 4. phase iia: either in good or stable health in the opinion of the investigator. participants may have underlying illness as long as their symptoms are medically controlled, and they are on a stable medication for the respective underlying illness for at least 8 weeks before screening and no changes are expected dur-ing the study. 5. body mass index 18.5 - 32.0 kg/m2 and weight > 50 kg at screening. 6. female participants: non-pregnant, non-lactating with negative pregnancy test. 7. females who agree to comply with the applicable contraceptive requirements of the protocol. 8. documented previous sars-cov-2 infection (pcr-positive) or documented vaccination against sars-cov-2 with (conditionally) licensed vaccine against covid-19, at least 6 months prior to in-clusion into this study. (phase iia open-label only)