A Phase 3 Trial of the VLP-Based Chikungunya Vaccine PXVX0317 (CHIKV VLP Vaccine)

Coprimary Objectives: 1. To evaluate the safety of PXVX0317 (CHIKV VLP vaccine) in healthy adult and adolescent participants 12 to \<65 years of age. 2. To compare the anti-CHIKV serum neutralizing antibody (SNA) response to PXVX0317 (CHIKV VLP vaccine) and placebo at Day 22, as measured by geometric mean titer (GMT) and clinically relevant difference in seroresponse rate (PXVX0317 minus placebo). 3. To demonstrate the consistency of the anti-CHIKV SNA response across three consecutively manufactured lots of PXVX0317 (CHIKV VLP vaccine) at Day 22 as measured by GMT. Secondary Objectives: 1. To compare the anti-CHIKV SNA response to PXVX0317 (CHIKV VLP vaccine) and placebo at Day 15, Day 183, and Day 8 as measured by GMT and seroresponse rate. 2. To compare the GMT fold increase in anti-CHIKV SNA response and number and percentage of participants with an anti-CHIKV SNA titer ≥15 and 4-fold rise over baseline, both at Day 8, 15, 22, and 183.