VLA2001 Booster in Adult Participants After Priming With mRNA COVID-19 Vaccine and/or 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 Exclusion Criteria: ALL PARTICIPANTS: 1. Participant is pregnant or planning to become pregnant within 3 months after booster administration 2. History of allergy to any component of the vaccine 3. Participant had close contact to persons with confirmed SARS-CoV-2 infection within 30 days prior to screening (Visit 0) 4. Participant has participated in a clinical study involving an investigational SARS-CoV-2 vaccine or has received or plans to receive a licensed SARS-CoV-2 vaccine during the duration of the study 5. Significant infection or other acute illness, including fever \> 37.8 °C within 48 hours before vaccination 6. Positive SARS-CoV-2 rapid Antigen test result during screening or Visit 1 7. Participant has a known or suspected defect of the immune system, such as participants with congenital or acquired immunodeficiency, including infection with HIV, status post organ transplantation or immuno-suppressive therapy within 4 weeks prior to the expected day of vaccination (Visit 1). 8. Participant has a history of malignancy in the past 5 years other than squamous cell or basal cell skin cancer. If there has been surgical excision or treatment more than 5 years ago that is considered to have achieved a cure, the participant may be enrolled. 9. History of drug dependency or current use of drug of abuse or alcohol abuse at screening 10. Significant blood loss (\> 450 mL) or has donated 1 or more units of blood or plasma within 6 weeks prior to the expected day of first vaccination (Visit 1) 11. History of clinically significant bleeding disorder (e.g., factor deficiency, coagulopathy, or platelet disorder), or prior history of significant bleeding or bruising following IM injections or venepuncture 12. Severe and uncontrolled ongoing autoimmune or inflammatory disease, History of Guillain-Barre syndrome or any other demyelinating condition 13. Any other significant disease, disorder or finding which in the opinion of the investigator may significantly increase the risk to the volunteer because of participation in the study, affect the ability of the volunteer to participate in the study or impair interpretation of the study Prior/concomitant therapy: 14. Receipt of immunoglobulin or another blood product within the 3 months before expected day of vaccination (Visit 1) in this study or those who expect to receive immunoglobulin or another blood product during this study 15. Receipt of medications to treat or prevent COVID-19 (except licensed mRNA vaccine for participants of cohort 1 and 2) 16. Receipt of any vaccine (licensed or investigational), other than licensed influenza vaccine or for medical emergencies such as tetanus or rabies exposure, within 28 days prior to the expected day of first vaccination (Visit 1) Others: 17. Any member of the study team or sponsor 18. An immediate family member or household member of the study's personnel