In this open-label Phase 3b, single-arm study, persistence of antibodies and long term safety in up to 375 subjects rolled over from study VLA1553-301 (NCT number: NCT04546724)

These subjects will have annual follow-up visits at Months 12, 24, 36, 48 and 60 after immunization. The primary objective of this study will be to evaluate persistence of antibodies annually from 1 to 5 years after the single immunization with VLA1553. The secondary objective is to evaluate long-term safety 6 months to 2 years after the single immunization with VLA1553.