The study will investigate the immunogenicity and safety of VLA84 up to six months after the last vaccination, i.e. 210 days per subject. The study includes eight outpatient visits on days 0, 7, 14, 28, 35, 56, 120 and 210. Serum will be collected to assess humoral immunity at days 0, 7, 14, 28, 35, 56, 120 and 210.