Publication date: Dec 31, 2024

This phase 1, open-label, dose-escalation, multi-center study (NCT05477186) assessed the safety and immunogenicity of a booster dose of an mRNA COVID-19 vaccine (CV0501) encoding the SARS-CoV-2 Omicron BA. 1 spike protein. Participants aged ≥ 18 years previously vaccinated with ≥ 2 doses of an mRNA COVID-19 vaccine received CV0501 doses ranging from 12 to 200 μg. After assessment of safety and immunogenicity of the 12 μg dose in 30 adults, 30 adults ≤ 64 years were randomized to receive either a 3 or 6 μg dose. Solicited adverse events (AEs) were collected for 7 days, unsolicited AEs for 28 days, and serious AEs (SAEs), medically attended AEs (MAAEs), and AEs of special interest (AESIs) until day (D) 181 post-vaccination. Serum neutralizing titers specific to SARS-CoV-2 BA. 1, wild-type, Delta, and additional Omicron subvariants were assessed at D1, D15, D29, D91, and D181. Of 180 vaccinated participants (mean age: 49. 3 years; 57. 8% women), 70. 6% had prior SARS-CoV-2 infection. Most solicited local (98. 1%) and systemic (96. 7%) AEs were of mild-to-moderate severity; the most common were injection site pain (57. 5%; 33. 3-73. 3% across groups) and myalgia (36. 9%; 13. 3-56. 7%). Unsolicited AEs were reported by 14. 4% (6. 7-26. 7%) of participants (mild-to-moderate severity in 88. 5% of the participants). Three participants (1. 7%) reported SAEs, 16. 7% (6. 7-30. 0%) reported MAAEs, and 8. 3% (0. 0-13. 3%) reported AESIs (15 COVID-19 cases), none related to vaccination. Geometric means of serum neutralizing titers increased from baseline to D15 and D29 (dose-dependent), and then decreased over time. The safety and immunogenicity results supported advancement to a phase 2 trial.

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