inclusion criteria: the subject must not be enrolled before all inclusion criteria (including test results) are confirmed. subjects meeting all of the criteria listed below will be included in the study. 1. signed written informed consent from subject prior to any study-related procedure and willingness to comply with treatment and follow-up procedures 2. healthy men or women, aged ≥ 18 ≤ 60 at day of inclusion having received either 1. primary immunization (cohort 1) with any regimen using any eu marketed sars- cov-2 vaccine or 2. subsequently booster immunization (cohort 2) with any eu marketed mrna vaccine at least 3 months prior to enrollment 3. adults with sars-cov-2 specific igg concentration between 10 ru/ml and 1200 ru/ml determined by anti-sars-cov-2-quantivac-elisa (igg) 4. males or non-pregnant, non-lactating females of child-bearing potential with negative pregnancy test at screening who agree to comply with the applicable contraceptive requirements of the protocol (section 3.4) from at least 14 days prior to vaccination and during the entire duration of the study. or females without child-bearing potential defined as follows: * at least 6 weeks after surgical sterilization by bilateral tubal ligation or bilateral oophorectomy or * hysterectomy or uterine agenesis or * ≥ 50 years and in postmenopausal state \> 1 year or * \< 50 years and in postmenopausal state \> 1 year with serum fsh \> 40 iu/l and serum estrogen \< 30 ng/l or a negative estrogen test, both at screening 5. normal pulmonary function: fev1 predicted ≥ 80% and fev1/fvc \> 70% 6. body mass index 18.5 - 30.0 kg/m2 and weight \> 50 kg at screening 7. subject is capable of understanding the investigational nature, potential risks and benefits of the clinical trial

inclusion criteria: the subject must not be enrolled before all inclusion criteria (including test results) are confirmed. subjects meeting all of the criteria listed below will be included in the study. 1. signed written informed consent from subject prior to any study-related procedure and willingness to comply with treatment and follow-up procedures 2. healthy men or women, aged ≥ 18 ≤ 60 at day of inclusion having received either 1. primary immunization (cohort 1) with any regimen using any eu marketed sars- cov-2 vaccine or 2. subsequently booster immunization (cohort 2) with any eu marketed mrna vaccine at least 3 months prior to enrollment 3. adults with sars-cov-2 specific igg concentration between 10 ru/ml and 1200 ru/ml determined by anti-sars-cov-2-quantivac-elisa (igg) 4. males or non-pregnant, non-lactating females of child-bearing potential with negative pregnancy test at screening who agree to comply with the applicable contraceptive requirements of the protocol (section 3.4) from at least 14 days prior to vaccination and during the entire duration of the study. or females without child-bearing potential defined as follows: * at least 6 weeks after surgical sterilization by bilateral tubal ligation or bilateral oophorectomy or * hysterectomy or uterine agenesis or * ≥ 50 years and in postmenopausal state \> 1 year or * \< 50 years and in postmenopausal state \> 1 year with serum fsh \> 40 iu/l and serum estrogen \< 30 ng/l or a negative estrogen test, both at screening 5. normal pulmonary function: fev1 predicted ≥ 80% and fev1/fvc \> 70% 6. body mass index 18.5 - 30.0 kg/m2 and weight \> 50 kg at screening 7. subject is capable of understanding the investigational nature, potential risks and benefits of the clinical trial

inclusion criteria: the subject must not be enrolled before all inclusion criteria (including test results) are confirmed. subjects meeting all of the criteria listed below will be included in the study. signed written informed consent from subject prior to any study-related procedure and willingness to comply with treatment and follow-up procedures healthy men or women, aged ≥ 18 ≤ 60 at day of inclusion having received either primary immunization (cohort 1) with any regimen using any eu marketed sars- cov-2 vaccine or subsequently booster immunization (cohort 2) with any eu marketed mrna vaccine at least 3 months prior to enrollment adults with sars-cov-2 specific igg concentration between 10 ru/ml and 1200 ru/ml determined by anti-sars-cov-2-quantivac-elisa (igg) males or non-pregnant, non-lactating females of child-bearing potential with negative pregnancy test at screening who agree to comply with the applicable contraceptive requirements of the protocol (section 3.4) from at least 14 days prior to vaccination and during the entire duration of the study. or females without child-bearing potential defined as follows: at least 6 weeks after surgical sterilization by bilateral tubal ligation or bilateral oophorectomy or hysterectomy or uterine agenesis or ≥ 50 years and in postmenopausal state > 1 year or < 50 years and in postmenopausal state > 1 year with serum fsh > 40 iu/l and serum estrogen < 30 ng/l or a negative estrogen test, both at screening normal pulmonary function: fev1 predicted ≥ 80% and fev1/fvc > 70% body mass index 18.5 - 30.0 kg/m2 and weight > 50 kg at screening subject is capable of understanding the investigational nature, potential risks and benefits of the clinical trial

inclusion criteria: the subject must not be enrolled before all inclusion criteria (including test results) are confirmed. subjects meeting all of the criteria listed below will be included in the study. signed written informed consent from subject prior to any study-related procedure and willingness to comply with treatment and follow-up procedures healthy men or women, aged ≥ 18 ≤ 60 at day of inclusion having received either primary immunization (cohort 1) with any regimen using any eu marketed sars- cov-2 vaccine or subsequently booster immunization (cohort 2) with any eu marketed mrna vaccine at least 3 months prior to enrollment adults with sars-cov-2 specific igg concentration between 10 ru/ml and 1200 ru/ml determined by anti-sars-cov-2-quantivac-elisa (igg) males or non-pregnant, non-lactating females of child-bearing potential with negative pregnancy test at screening who agree to comply with the applicable contraceptive requirements of the protocol (section 3.4) from at least 14 days prior to vaccination and during the entire duration of the study. or females without child-bearing potential defined as follows: at least 6 weeks after surgical sterilization by bilateral tubal ligation or bilateral oophorectomy or hysterectomy or uterine agenesis or ≥ 50 years and in postmenopausal state > 1 year or < 50 years and in postmenopausal state > 1 year with serum fsh > 40 iu/l and serum estrogen < 30 ng/l or a negative estrogen test, both at screening normal pulmonary function: fev1 predicted ≥ 80% and fev1/fvc > 70% body mass index 18.5 - 30.0 kg/m2 and weight > 50 kg at screening subject is capable of understanding the investigational nature, potential risks and benefits of the clinical trial

inclusion criteria: the subject must not be enrolled before all inclusion criteria (including test results) are confirmed. subjects meeting all of the criteria listed below will be included in the study. signed written informed consent from subject prior to any study-related procedure and willingness to comply with treatment and follow-up procedures healthy men or women, aged ≥ 18 ≤ 60 at day of inclusion having received either primary immunization (cohort 1) with any regimen using any eu marketed sars- cov-2 vaccine or subsequently booster immunization (cohort 2) with any eu marketed mrna vaccine at least 3 months prior to enrollment adults with sars-cov-2 specific igg concentration between 10 ru/ml and 600 ru/ml determined by anti-sars-cov-2-quantivac-elisa (igg) males or non-pregnant, non-lactating females of child-bearing potential with negative pregnancy test at screening who agree to comply with the applicable contraceptive requirements of the protocol (section 3.4) from at least 14 days prior to vaccination and during the entire duration of the study. or females without child-bearing potential defined as follows: at least 6 weeks after surgical sterilization by bilateral tubal ligation or bilateral oophorectomy or hysterectomy or uterine agenesis or ≥ 50 years and in postmenopausal state > 1 year or < 50 years and in postmenopausal state > 1 year with serum fsh > 40 iu/l and serum estrogen < 30 ng/l or a negative estrogen test, both at screening normal pulmonary function: fev1 predicted ≥ 80% and fev1/fvc > 70% body mass index 18.5 - 30.0 kg/m2 and weight > 50 kg at screening subject is capable of understanding the investigational nature, potential risks and benefits of the clinical trial

inclusion criteria: the subject must not be enrolled before all inclusion criteria (including test results) are confirmed. subjects meeting all of the criteria listed below will be included in the study. signed written informed consent from subject prior to any study-related procedure and willingness to comply with treatment and follow-up procedures healthy men or women, aged ≥ 18 ≤ 60 at day of inclusion having received either primary immunization (cohort 1) with any regimen using any eu marketed sars- cov-2 vaccine or subsequently booster immunization (cohort 2) with any eu marketed mrna vaccine at least 3 months prior to enrollment adults with sars-cov-2 specific igg concentration between 10 ru/ml and 600 ru/ml determined by anti-sars-cov-2-quantivac-elisa (igg) males or non-pregnant, non-lactating females of child-bearing potential with negative pregnancy test at screening who agree to comply with the applicable contraceptive requirements of the protocol (section 3.4) from at least 14 days prior to vaccination and during the entire duration of the study. or females without child-bearing potential defined as follows: at least 6 weeks after surgical sterilization by bilateral tubal ligation or bilateral oophorectomy or hysterectomy or uterine agenesis or ≥ 50 years and in postmenopausal state > 1 year or < 50 years and in postmenopausal state > 1 year with serum fsh > 40 iu/l and serum estrogen < 30 ng/l or a negative estrogen test, both at screening normal pulmonary function: fev1 predicted ≥ 80% and fev1/fvc > 70% body mass index 18.5 - 30.0 kg/m2 and weight > 50 kg at screening subject is capable of understanding the investigational nature, potential risks and benefits of the clinical trial

inclusion criteria: the subject must not be enrolled before all inclusion criteria (including test results) are confirmed. subjects meeting all of the criteria listed below will be included in the study. signed written informed consent from subject prior to any study-related procedure and willingness to comply with treatment and follow-up procedures healthy men or women, aged ≥ 18 ≤ 60 at day of inclusion completely immunized with homologous vaxzevria® or covid-19 vaccine janssen or comirnaty® at least 3 months prior to enrollment adults with sars-cov-2 specific igg concentration between 10 ru/ml and 300 ru/ml determined by anti-sars-cov-2-quantivac-elisa (igg) males or non-pregnant, non-lactating females of child-bearing potential with negative pregnancy test at screening who agree to comply with the applicable contraceptive requirements of the protocol (section 3.4) from at least 14 days prior to vaccination and during the entire duration of the study. or females without child-bearing potential defined as follows: at least 6 weeks after surgical sterilization by bilateral tubal ligation or bilateral oophorectomy or hysterectomy or uterine agenesis or ≥ 50 years and in postmenopausal state > 1 year or < 50 years and in postmenopausal state > 1 year with serum fsh > 40 iu/l and serum estrogen < 30 ng/l or a negative estrogen test, both at screening normal pulmonary function: fev1 predicted ≥ 80% and fev1/fvc > 70% body mass index 18.5 - 30.0 kg/m2 and weight > 50 kg at screening subject is capable of understanding the investigational nature, potential risks and benefits of the clinical trial

inclusion criteria: the subject must not be enrolled before all inclusion criteria (including test results) are confirmed. subjects meeting all of the criteria listed below will be included in the study. signed written informed consent from subject prior to any study-related procedure and willingness to comply with treatment and follow-up procedures healthy men or women, aged ≥ 18 ≤ 60 at day of inclusion completely immunized with homologous vaxzevria® or covid-19 vaccine janssen or comirnaty® at least 3 months prior to enrollment adults with sars-cov-2 specific igg concentration between 10 ru/ml and 300 ru/ml determined by anti-sars-cov-2-quantivac-elisa (igg) males or non-pregnant, non-lactating females of child-bearing potential with negative pregnancy test at screening who agree to comply with the applicable contraceptive requirements of the protocol (section 3.4) from at least 14 days prior to vaccination and during the entire duration of the study. or females without child-bearing potential defined as follows: at least 6 weeks after surgical sterilization by bilateral tubal ligation or bilateral oophorectomy or hysterectomy or uterine agenesis or ≥ 50 years and in postmenopausal state > 1 year or < 50 years and in postmenopausal state > 1 year with serum fsh > 40 iu/l and serum estrogen < 30 ng/l or a negative estrogen test, both at screening normal pulmonary function: fev1 predicted ≥ 80% and fev1/fvc > 70% body mass index 18.5 - 30.0 kg/m2 and weight > 50 kg at screening subject is capable of understanding the investigational nature, potential risks and benefits of the clinical trial