Using the vesicular stomatitis virus vector (rVSV vector) platform for SARS-CoV-2 vaccine development: Phase 1/2 safety and immunogenicity of IIBR-100 in healthy adults

Background: We investigated the safety and immunogenicity of the IIBR-100 (rVSV-SARS-CoV-2-S) vaccine, a recombinant VSV-ΔG-spike vaccine against SARS-CoV-2 virus. Methods: In a phase 1/2, randomized, observer-blind, placebo-controlled study (ClinicalTrials.gov: NCT 04608305), healthy younger (18–55 years) and older (56–85 years) adults were recruited from eight clinical sites in Israel. In the phase 1 study, low (1 × 10⁵ PFU), mid (1 × 10⁶ PFU), and high doses (1 × 10⁷ PFU) of IIBR-100 were tested in a single-dose treatment regimen, with an additional booster dose for the low-dose group only. Based on the phase 1 study results, only mid- and high-dose prime-boost regimens alongside an additional top dose (1 × 10⁸ PFU) were tested in the phase 2 study. Participants, randomly assigned to either IIBR-100 or placebo, were followed for 12 months from the last vaccination for safety and immunogenicity outcomes. Findings: No safety concerns were observed in the phase 1 study (N = 82); therefore, the study moved on to phase 2. In phase 2 (N = 762), for both age groups, the most common AEs included injection-site pain (20–64 %), fatigue (21–33 %), and headache (15–22 %). In the top-dose group, neutralizing and binding antibody titers peaked on Days 35 and 42, respectively; seroconversion rates reached maximal levels by Day 56 for neutralizing antibody and binding antibody (spike and RBD). Interpretation: The IIBR-100 vaccine against SARS-CoV-2 in prime-boost regimens at 1 × 10⁷ PFU/mL and 1 × 10⁸ PFU/mL doses is safe, well tolerated, and immunogenic in healthy adults. Clinical trial registry: This trial is registered at ClinicalTrials.gov (NCT 04608305) and in the trial registry of the Israeli Ministry of Health website.