Chikungunya Virus VLP Vaccine: Phase 3 Trial in Adults >= 65 Years of Age

1BackgroundAdults [≥]65 years of age are at increased risk for atypical presentations of chikungunya disease as well as severe outcomes including death. MethodsA phase 3, randomized, double-blind, placebo-controlled, parallel-group trial was conducted in adults [≥]65 years of age where participants received a single intramuscular dose of chikungunya virus (CHIKV) virus-like particle (VLP) vaccine or placebo on Day 1. Baseline and postvaccination CHIKV serum neutralizing antibody (SNA) titers (NT80) were assessed at selected timepoints. Safety was assessed through Day 183. ResultsA total of 413 participants (206 vaccine, 207 placebo) were randomized. Coprimary endpoints were met including 1) immunologic superiority of CHIKV SNA titers compared to placebo and 2) by geometric mean titer at Day 22. CHIKV VLP vaccine induced a protective seroresponse (SNA NT80 [≥]100; considered the presumptive seroprotective antibody response), in 82% of individuals at Day 15, in 87% of individuals at Day 22, and in 76% of individuals at Day 183. There were no notable differences in AE rates between groups and most AEs were grade 1 or 2 in severity. No vaccine-related serious adverse events or deaths occurred. ConclusionsWe provide robust data from adults [≥]65 years of age demonstrating that CHIKV VLP vaccine has a favorable safety profile and can provide a high rate of protection within 2 weeks postvaccination and through 6 months of follow-up. (Funded by Emergent BioSolutions Inc. and Bavarian Nordic A/S [as successor in interest to Emergent BioSolutions Inc.]; ClinicalTrials.gov number, NCT05349617).