One year antibody persistence and safety of a live-attenuated chikungunya virus vaccine candidate (VLA1553) in adults aged 18 years and above

Abstract

VLA1553 is a live-attenuated chikungunya virus (CHIKV) vaccine candidate designed for active immunization as a prophylactic measure for individuals travelling to or living in endemic areas. Due to the sporadic epidemic occurrence of chikungunya, an immunological surrogate to assess clinical efficacy was accepted by regulators (FDA and EMA). To evaluate persistence of antibodies annually from 1 to at least 5 years after a single immunization with VLA1553. This phase 3 open-label, single arm long term antibody persistence and safety trial (VLA1553-303) follows a subset (N=363) of VLA1553 vaccinees from the pivotal phase 3 trial (VLA1553-301) where 4,115 adult participants received VLA1553 or placebo. The main aim of VLA1553-303 is to annually assess (at least until Year 5) the proportion of participants from study VLA1553-301 with seroresponse (defined as μPRNT ≥150). Additionally, the frequency and relatedness of any serious adverse event (SAE) until Year 2 is monitored. This presentation outlines the immunogenicity and safety data collected until Year 1. VLA1553-303 met its primary endpoint with a participant seroresponse rate of 98.9% at Year 1. Regarding GMTs, the initial Day 29 GMT for the group followed in the long term study was 3489 and remained high, with 1009 at Day 180 and 1056 at Year 1. Moreover, in older adults aged ≥65 years, antibody persistence was similar to younger adults throughout the follow-up. Four SAEs were reported in participants in study VLA1553-303 from 6 to 12 months post-vaccination. All cases were assessed as not related by the investigators, furthermore there was no persistent adverse event of special interest thus confirming that no safety concern was identified in study VLA1553-303 until Year 1. VLA1553-303 demonstrated that antibody persistence was confirmed at Year 1 post-vaccination as a high seroresponse was maintained throughout the study. Furthermore, no safety concern was identified with all four SAEs being assessed as not related by the investigators; the safety profile from earlier studies was confirmed. This study further reinforces the VLA1553-301 results showing VLA1553 as a possible effective prevention of CHIKV disease. R. M. Valneva Austria GmbH, Vienna, Austria S. T. Valneva Austria GmbH, Vienna, Austria M. S. Valneva Austria GmbH, Vienna, Austria S. H. Valneva Austria GmbH, Vienna, Austria R. H. Valneva Austria GmbH, Vienna, Austria K. K. Valneva Austria GmbH, Vienna, Austria R. M. Valneva Austria GmbH, Vienna, Austria O. Z. Valneva Austria GmbH, Vienna, Austria N. W. Valneva Austria GmbH, Vienna, Austria K. D. Valneva Austria GmbH, Vienna, Austria V. B. Valneva Austria GmbH, Vienna, Austria S. E. Valneva Austria GmbH, Vienna, Austria J.C. J Valneva Austria GmbH, Vienna, Austria