Chikungunya Virus VLP Vaccine: Phase 3 Trial in Adolescents and Adults

1 ABSTRACT Background Chikungunya disease is a growing global public health concern. Chikungunya virus (CHIKV) virus-like particle (VLP) vaccine is a single dose, pre-filled syringe for intramuscular injection. Methods A pivotal phase 3 randomized, double-blind, placebo-controlled trial was conducted in healthy adolescents and adults 12-64 years of age. Participants received either CHIKV VLP vaccine or placebo on Day 1. Immunogenicity objectives assessed CHIKV serum neutralizing antibody (SNA) titers (NT 80 ) at selected timepoints. Safety was assessed through Day 183 postvaccination. Results A total of 2790 participants received CHIKV VLP vaccine and 464 received placebo (n=3454). Coprimary endpoints were met including 1) immunologic superiority to placebo and 2) geometric mean titer at Day 22. Results demonstrated that CHIKV VLP vaccine induced a protective seroresponse (SNA NT 80 ≥100; considered the presumptive seroprotective antibody response), in 97% of individuals at Day 15 (2 weeks), in 98% of individuals at Day 22, and in 86% of individuals at Day 183 (6 months). CHIKV VLP vaccine demonstrated a favorable safety profile. The majority of adverse events were self-limited and grade 1 or 2 in severity. The most common adverse events were injection site pain, fatigue, headache, and myalgia. Conclusions CHIKV VLP vaccine induces a rapid and robust immune response by Day 15 that lasts through Day 183 postvaccination. These findings support the potential for this vaccine to protect individuals 12-64 years of age from disease caused by CHIKV. (Funded by Emergent BioSolutions Inc. and Bavarian Nordic A/S [as successor in interest to Emergent BioSolutions Inc.]; ClinicalTrials.gov number, NCT05072080 ).