A phase 3, randomised, observer-blinded, placebo controlled-trial evaluating the safety and immunogenicity of investigational SARS-CoV-2 mRNA vaccine CVnCoV in adult healthcare workers in Mainz (Germany)

Background

CV-NCOV-005 was conducted to generate additional safety and immunogenicity data for the former CVnCoV SARS-CoV-2 mRNA vaccine candidate in healthcare workers (HCW).

Methods

Randomised, observer blinded, placebo-controlled, phase 3 trial performed at the University Medical Center Mainz, Germany. HCWs aged ≥18 years with no history of SARS-CoV-2 infection/positive serology were randomly assigned to receive two doses of CVnCoV, or two doses of placebo (0.9% NaCl). The primary objectives were to expand the safety database of CVnCoV and assess antibody responses against SARS-CoV-2. Primary safety and reactogenicity outcomes included solicited adverse events (AEs) within 7 days after each dose and unsolicited AEs within 28 days after each dose, with safety follow-up for 13 months after first vaccination. Since HCWs became eligible to receive an authorised vaccine during enrolment and efficacy results from HERALD CVnCoV trial were made available on 30^th of June 2021, this study was unblinded and converted to an open label design.

Results

Most participants in the CVnCoV group reported at least one solicited AE, a relatively high number being Grade 3 (43.3% in CVnCoV group and 6.4% in placebo group). Most AEs were short in duration and did not affect vaccine compliance. The percentage of participants with unsolicited AEs up to 28 days after any dose was slightly higher in CVnCoV group (37.0%) compared with placebo group (31.2%). IgG binding antibodies against the receptor binding domain of the SARS-CoV-2 spike protein were observed after vaccination, with higher seroconversion rates and antibody levels after the second dose.

Conclusion

No safety concerns for CVnCoV were identified up to 1 year post second dose. IgG responses against SARS-CoV-2 were observed after two doses, with a higher seroconversion rate and antibody levels observed after second vaccination.

Study registration: ClinicalTrials.gov NCT04674189, study period: 23^rd of December 2020 to 8^th of June 2022.