Phase I study of a SARS-CoV-2 mRNA vaccine PTX-COVID19-B

PTX-COVID19-B mRNA vaccine encodes for SARS-CoV-2 Spike protein G614 variant and lacks the proline-proline (986-987 position) mutation present in other COVID-19 vaccines. This Phase 1 observer-blinded, randomized, placebo-controlled, ascending dose study evaluated the safety, tolerability, and immunogenicity of two doses of PTX-COVID19-B vaccine in healthy seronegative adults. Participants received two intramuscular doses, 4 weeks apart, of 16-g, 40-g, or 100-g PTX-COVID19-B. Adverse events were generally mild to moderate, self-resolving, and transient. The most common solicited local and systemic adverse event was pain at the injection site and headache, respectively. After the first immunization, all participants seroconverted, producing high titers of anti-receptor-binding-domain, anti-Spike, and neutralizing antibodies, including neutralizing antibodies against the ancestral viral strain and the Alpha, Beta, and Delta variants of concern, in a dose-dependent way, further increasing over 10-20 times after the second dose. All tested doses of PTX-COVID19-B were safe, well-tolerated, and provided a strong immunogenicity response. The 40-g dose showed fewer adverse reactions than the 100-g dose, supporting further investigation of the 40-g dose. Clinical Trial RegistrationClinicalTrials.gov identifier: NCT04765436 (https://clinicaltrials.gov/ct2/show/NCT04765436)