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