Phase 1 Trial to Assess the Safety and Immunogenicity of an Inactivated, Adjuvanted Whole Zika Virus Vaccine Candidate (VLA1601) in Healthy Adults

VLA1601 is a second generation, highly purified, inactivated, whole ZIKV vaccine candidate (adsorbed on aluminum hydroxide) designed for active immunization for the prevention of disease caused by the flavivirus ZIKV. This is a phase 1 trial, consisting of an initial open-label sentinel run-in (n=25) phase and a randomized, double-blind, dose-finding trial (n=125) in flavivirus naïve adults aged 18 to 49 years. In total approximately 150 participants will be vaccinated in this trial. The trial will investigate three antigen dose levels (low, medium and high) of VLA1601. In addition, CpG 1018® or 3M-052-AF/AP 60-702 are investigated as add-on adjuvants in the low dose group (bedside mixing). Each dose is formulated with alum (aluminum hydroxide) adjuvant. In each of the five treatment arms 30 participants (each with 5 sentinel/run-in and 25 randomized participants) will be vaccinated. Each participant will receive 2 vaccinations, one on Day 1 and one on Day 29, which will be administered intramuscularly (i.m.) in the deltoid muscle (non-dominant arm). The screening period can last up to 21 days. The trial began with the vaccination of 25 sentinel participants (5 participants in each of the 5 treatment arms) in a sequential open-label, staggered dose-escalation manner. Up to approximately 125 participants will be randomized 1:1:1:1:1, stratified by trial site to 5 treatment arms. The injection volume in each treatment arm will be 0.45 mL at each of the 2 vaccinations. The primary objective of this trial is to assess the safety and tolerability of the vaccine candidate up to 7 days after each vaccination; and to assess the immune response induced by the vaccine candidate 28 days after the second vaccination. Following a sponsor review of available safety and immunogenicity data up to 6 months after the second vaccination, all sentinels and randomized participants from most favorable treatment arm(s) will be selected for an on-site visit at Day 395 for long-term safety and immunogenicity assessment. All other treatment arms will be followed only by phone-call for the Day 395 assessment of long-term safety.