inclusion criteria: all participants: 1. participants of either gender aged 18 years and older at screening 2. participants must have read, understood, and signed the informed consent form (icf) 3. medically stable 4. participant has a body mass index (bmi) of 18.0-30.0 kg/m2 5. must be able to attend all visits of the study and comply with all study procedures 6. women of childbearing potential (wocbp) must be able and willing to use at least 1 highly effective method of contraception 7. wocbps must have a negative pregnancy test prior to the booster vaccination. cohort 1: will receive a standard dose of vla2001 (0.5 ml), if: * aged between 18 years and 50 years and * have received two or three doses of mrna sars-cov-2 vaccines and have never experienced a natural sars-cov-2 infection, or * have received two or three doses of mrna sars-cov-2 vaccines and have experienced a natural sars-cov-2 infection. cohort 2: will receive a double dose of vla2001 (1.0 ml), if: * older than 50 years and * have received two or three doses of mrna sars-cov-2 vaccines and have never experienced a natural sars-cov-2 infection, or * have received two or three doses of mrna sars-cov-2 vaccines and have experienced a natural sars-cov-2 infection. cohort 3: will receive a standard dose of vla2001 (0.5 ml), if: * aged between 18 years and 50 years and * have never received any sars-cov-2 vaccine and * have experienced a natural sars-cov-2 infection will receive a double dose of vla2001 (1.0 ml), if: * older than 50 years and * have never received any sars-cov-2 vaccine and * have experienced a natural sars-cov-2 infection

inclusion criteria: all participants: 1. participants of either gender aged 18 years and older at screening 2. participants must have read, understood, and signed the informed consent form (icf) 3. medically stable 4. participant has a body mass index (bmi) of 18.0-30.0 kg/m2 5. must be able to attend all visits of the study and comply with all study procedures 6. women of childbearing potential (wocbp) must be able and willing to use at least 1 highly effective method of contraception 7. wocbps must have a negative pregnancy test prior to the booster vaccination. cohort 1: will receive a standard dose of vla2001 (0.5 ml), if: * aged between 18 years and 50 years and * have received two or three doses of mrna sars-cov-2 vaccines and have never experienced a natural sars-cov-2 infection, or * have received two or three doses of mrna sars-cov-2 vaccines and have experienced a natural sars-cov-2 infection. cohort 2: will receive a double dose of vla2001 (1.0 ml), if: * older than 50 years and * have received two or three doses of mrna sars-cov-2 vaccines and have never experienced a natural sars-cov-2 infection, or * have received two or three doses of mrna sars-cov-2 vaccines and have experienced a natural sars-cov-2 infection. cohort 3: will receive a standard dose of vla2001 (0.5 ml), if: * aged between 18 years and 50 years and * have never received any sars-cov-2 vaccine and * have experienced a natural sars-cov-2 infection will receive a double dose of vla2001 (1.0 ml), if: * older than 50 years and * have never received any sars-cov-2 vaccine and * have experienced a natural sars-cov-2 infection

inclusion criteria: all participants: participants of either gender aged 18 years and older at screening participants must have read, understood, and signed the informed consent form (icf) medically stable participant has a body mass index (bmi) of 18.0-30.0 kg/m2 must be able to attend all visits of the study and comply with all study procedures women of childbearing potential (wocbp), must be able and willing to use at least 1 highly effective method of contraception wocbps must have a negative pregnancy test prior to the booster vaccination. cohort 1: will receive a standard dose of vla2001 (0.5 ml), if: aged between 18 years and 50 years and have received two or three doses of mrna sars-cov-2 vaccines and have never experienced a natural sars-cov-2 infection, or have received two or three doses of mrna sars-cov-2 vaccines and had experienced a natural sars-cov-2 infection. cohort 2: will receive a double dose of vla2001 (1.0 ml), if: older than 50 years and have received two or three doses of mrna sars-cov-2 vaccines and have never experienced a natural sars-cov-2 infection, or have received two or three doses of mrna sars-cov-2 vaccines and had experienced a natural sars-cov-2 infection. cohort 3: will receive a standard dose of vla2001 (0.5 ml), if: aged between 18 years and 50 years and have never received any sars-cov-2 vaccine and have experienced a natural sars-cov-2 infection will receive a double dose of vla2001 (1.0 ml), if: older than 50 years and have never received any sars-cov-2 vaccine and have experienced a natural sars-cov-2 infection

inclusion criteria: all participants: participants of either gender aged 18 years and older at screening participants must have read, understood, and signed the informed consent form (icf) medically stable participant has a body mass index (bmi) of 18.0-30.0 kg/m2 must be able to attend all visits of the study and comply with all study procedures women of childbearing potential (wocbp), must be able and willing to use at least 1 highly effective method of contraception wocbps must have a negative pregnancy test prior to the booster vaccination. cohort 1: will receive a standard dose of vla2001 (0.5 ml), if: aged between 18 years and 50 years and have received two or three doses of mrna sars-cov-2 vaccines and have never experienced a natural sars-cov-2 infection, or have received two or three doses of mrna sars-cov-2 vaccines and had experienced a natural sars-cov-2 infection. cohort 2: will receive a double dose of vla2001 (1.0 ml), if: older than 50 years and have received two or three doses of mrna sars-cov-2 vaccines and have never experienced a natural sars-cov-2 infection, or have received two or three doses of mrna sars-cov-2 vaccines and had experienced a natural sars-cov-2 infection. cohort 3: will receive a standard dose of vla2001 (0.5 ml), if: aged between 18 years and 50 years and have never received any sars-cov-2 vaccine and have experienced a natural sars-cov-2 infection will receive a double dose of vla2001 (1.0 ml), if: older than 50 years and have never received any sars-cov-2 vaccine and have experienced a natural sars-cov-2 infection

inclusion criteria: all participants: participants of either gender aged 18 years and older at screening participants must have read, understood, and signed the informed consent form (icf) medically stable participant has a body mass index (bmi) of 18.0-30.0 kg/m2 must be able to attend all visits of the study and comply with all study procedures women of childbearing potential (wocbp), must be able and willing to use at least 1 highly effective method of contraception wocbps must have a negative pregnancy test prior to the booster vaccination. only applicable for cohort "mrna primed": has received a second dose of licensed mrna covid-19 vaccine 6 to 12 months before study vaccination only applicable for cohort "naturally primed": pcr confirmed natural sars-cov-2 infection 6 to 12 months before study vaccination

inclusion criteria: all participants: participants of either gender aged 18 years and older at screening participants must have read, understood, and signed the informed consent form (icf) medically stable participant has a body mass index (bmi) of 18.0-30.0 kg/m2 must be able to attend all visits of the study and comply with all study procedures women of childbearing potential (wocbp), must be able and willing to use at least 1 highly effective method of contraception wocbps must have a negative pregnancy test prior to the booster vaccination. only applicable for cohort "mrna primed": has received a second dose of licensed mrna covid-19 vaccine 6 to 12 months before study vaccination only applicable for cohort "naturally primed": pcr confirmed natural sars-cov-2 infection 6 to 12 months before study vaccination