BMC infectious diseasesNov 21, 2025

Safety, immune response, lasting effects, and dose testing of the CS-2034 mRNA COVID-19 vaccine in healthy Chinese adults

mRNA Technology Weekly Brief ↗PubMed ↗DOI ↗OA ↗

Updated Jun 28, 2026

Abstract

Essence

In healthy Chinese adults, the CS-2034 mRNA COVID-19 vaccine induced strong and persistent antibodies to ancestral SARS-CoV-2, with the 0.3 mL dose favored for further development.

Evidence

This phase II multicenter randomized, double-blind, placebo-controlled dose trial in 150 healthy Chinese adults found mild to moderate reactogenicity and strong neutralizing antibody responses at both vaccine doses.

Caveat

Neutralizing activity against the Omicron BA.1 variant was limited and declined after the peak response.

Simplified

BACKGROUND: 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.

METHODS: 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).

RESULTS: 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.

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

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

Key numbers

80.00%

Adverse Event Incidence Rate (Low-Dose)

Incidence rate of adverse events in the low-dose vaccine group.

100.00%

Seroconversion Rate Against Original Strain

Seroconversion rate for neutralizing antibodies at 28 days after vaccination in both vaccine groups.

10.00%

Seroconversion Rate Against Omicron BA.1 Variant

Seroconversion rate for neutralizing antibodies against the Omicron BA.1 variant at 28 days post-vaccination.

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Safety, immune response, lasting effects, and dose testing of the CS-2034 mRNA COVID-19 vaccine in healthy Chinese adults

Abstract

Key numbers

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