Valneva SE announced positive Phase 1 interim results for its Chikungunya vaccine candidate, VLA1553. The primary objective of VLA1553-101 Phase 1 study was to assess the overall safety and immunogenicity profile 28 days after a single vaccination across three dose levels. The interim results showed an excellent immunogenicity profile after a single vaccination with a 100% seroconversion rate achieved at Day 28 in a pooled analysis of all vaccinated groups. Results also showed 96.5% of subjects achieved at least a 16-fold increase in antibody titres and a high geometric mean titre, fully supporting VLA1553's differentiated target product profile. The pooled safety profile of all groups was considered acceptable and supports further development. No serious adverse events nor adverse events of special interest were reported up to Day 28 and the local tolerability was considered excellent. Systemic adverse events included short-term fever, headache and fatigue. As with other live-attenuated vaccines, transient cases of reduced levels of neutrophils, lymphocytes or leucocytes without clinical symptoms were observed in the pooled analysis. This study is a randomized, observer-blinded, multicenter, dose-escalation Phase 1 clinical study investigating three dose levels of VLA1553 after a single immunization. The study enrolled 120 healthy volunteers, 18 to 45 years of age, in the United States. Subjects were randomized in three different study groups to receive one of three dose levels (30 subjects in the low and medium and 60 subjects in the high dose group). The protocol includes a re-vaccination at Month 6 or Month 12 to confirm that a single vaccination will be sufficient to induce high titer neutralizing antibodies and protect subjects from Chikungunya viremia (intrinsic viral challenge). Study participants will be followed up until 13 months after initial vaccination. The interim results included blinded, pooled safety and immunogenicity data up to Day 28. It did not provide group specific information or formal primary endpoint read-out. An independent Drug Safety Monitoring Board (DSMB) continuously oversees the study and reviews data.