VLA2001 Booster in Adult Participants After Priming With mRNA COVID-19 Vaccine and/or Natural SARS-CoV-2 Infection

This is a multicentric, open-label, phase 2/3 study to investigate the safety, tolerability and immunogenicity of a VLA2001 booster vaccination standard dose in adults aged ≥18 to ≤50 years or double dose in volunteers aged \>50 years. Volunteers who are either generally healthy or are with a stable medical condition will be enrolled. In total approximately 275 participants were planned to be enrolled. It was planned to enroll approximately 25% of participants who are above 65 years into the cohorts with participants above 50 years of age. Cohorts 1B, 1C, 1D, 2B and 2D have been fully recruited. Recruitment for Cohorts 1A, 2A, 2C, and 3, has been stopped in December 2022 due to very low recruitment rates in these cohorts. The revised study design ensures a safety follow-up of at least 6 months after the VLA2001 vaccination for all enrolled study participants. Immunogenicity will be assessed at Visits 1 (pre-booster, Day 1) and Visit 2 (Day 15, 14 days after the booster vaccination). Safety will be assessed up to Visit 3a (Day 180) or up to an End of Study Visit for participants who have already had their Day 180 visit before the current study amendment.