This is a prospective, double-blinded, multicenter, randomized, pivotal Phase 3 study comprising approximately 4,060 subjects aged 18 years or above randomized in a 3:1 ratio to the live-attenuated CHIKV vaccine candidate (VLA1553) or placebo. The final dose of lyophilized VLA1553 or placebo will be administered as a single intramuscular immunization. Subjects in this study will be stratified into two age strata of 18 to 64 years and 65 years of age or above. The primary objective of the study is to evaluate the immunogenicity and safety of the final dose of VLA1553 28 days following the single immunization. Immunogenicity evaluations in the immunogenicity subset will include the proportion of subjects with seroprotective neutralizing CHIKV antibody titers above a surrogate threshold indicative of protection. The surrogate of protection reasonably likely to predict clinical benefit has been established in non-human primate passive transfer studies using human sera from the Phase 1 study. Safety data collection and immunogenicity will continue to be assessed until Month 6~The first enrolled and randomized approximately 500 subjects will comprise the immunogenicity subset.
This is a prospective, randomized, double-blinded, multicenter, pivotal clinical study evaluating the final dose of VLA1553 (1 x10E4 TCID50 per dose) in comparison to a placebo control. The final dose of VLA1553 or control will be administered as single immunization on Day 1. Overall, approximately 4,060 male and female subjects aged 18 years and above will be enrolled into the study.