Safety, immunogenicity, persistence and dose evaluation of the CS-2034 mRNA COVID-19 vaccine: a phase II randomized...

Our objective was to evaluate the safety and immunogenicity of the COVID-19 mRNA vaccine (CS-2034) in Chinese adults, and to determine the optimal dosage with a favorable safety and immunogenicity profile.

This study was a phase II clinical trial conducted across multiple centers, employing a randomized, double-blinded, dose-exploration, placebo-controlled design which was registered at ClinicalTrials.gov under the identifier NCT05373472 (registration date: May 13, 2022).

A total of 150 participants were randomized into low-dose vaccine, high-dose vaccine, and placebo groups. The vaccine CS-2034 was well tolerated, with adverse reactions largely mild to moderate and comparable across dose groups. Both dose levels induced strong neutralizing antibody responses against the ancestral SARS-CoV-2 strain, with high seroconversion and evidence of antibody persistence over time. In contrast, neutralizing activity against the Omicron BA.1 variant was limited and declined further after the peak response.

The 0.3 mL dose (low-dose vaccine) was selected for further development based on comparable immunogenicity and lower reactogenicity.

The study was registered at ClinicalTrials.gov under the identifier NCT05373472 (registration date: May 13, 2022).