0204: Immunogenicity and safety summary for the chikungunya virus-like particle vaccine development programme

Background/Purpose: Chikungunya virus (CHIKV) is a threat to public health and a risk for travellers to endemic countries. Typical acute symptoms include fever, arthralgia, myalgia, fatigue, and headache. Debilitating arthralgias may persist for months or years. We report aggregated safety and immunogenicity data from five clinical trials for a CHIKV virus-like particle (VLP) vaccine, which has been approved for use by the US FDA in February 2025.

Methods: To date, the CHIKV VLP vaccine development programme has included three phase 2 and two phase3 trials across multiple sites in the US, which enrolled participants 12 to 95 years of age. Participants received a single dose of CHIKV VLP vaccine or placebo. The safety population included 3141vaccinated and 675 placebo participants from five trials and the immunogenicity evaluable population included 2829 vaccinated and 607 placebo participants from four trials. Immunogenicity was assessed by measuring CHIKV serum neutralising antibody (SNA) titres (NT80) at selected time points; SNANT80 ≥100 is the surrogate marker likely to predict protection. Immunogenicity and safety were assessed through Day 183 post vaccination.

Results: Immunogenicity findings showed robust responses, with a seroresponse (SNA NT80 ≥100) as early as Day 8 (47%), peaking at Day 15 (96%) and Day 22 (97%; primary endpoint), and lasting through Day183 (85%).In phase 3 trials, the seroresponse rate and geometric mean titre was significantly higher in the vaccine group than the placebo group at all time points. CHIKV VLP vaccine demonstrated a favourable safety profile across trials. Most AEs were mild or moderate; events primarily consisted of injection site pain, headache, fatigue, and myalgia. Solicited and unsolicited events of arthralgia were reported at similar rates between vaccinated and placebo participants. SAEs occurred in < 1% of participants, with no vaccine-related deaths. Overall, no safety signals were detected.

Conclusion: CHIKV VLP vaccine offers a VLP-based vaccine option for immunisation against CHIKV disease. The data analysed demonstrate the strong immunogenicity and favourable safety profile of CHIKV VLP vaccine; rapid and durable SNA NT80 responses support the potential for this vaccine to protect individuals ≥12 years of age from disease caused by CHIKV.