Safety and immunogenicity of an mRNA-lipid nanoparticle vaccine candidate against SARS-CoV-2 : A phase 1 randomized clinical trial

Wien Klin Wochenschr. 2021 Sep;133(17-18):931-941. doi: 10.1007/s00508-021-01922-y. Epub 2021 Aug 10.


Background: We used the RNActive® technology platform (CureVac N.V., Tübingen, Germany) to prepare CVnCoV, a COVID-19 vaccine containing sequence-optimized mRNA coding for a stabilized form of SARS-CoV‑2 spike (S) protein encapsulated in lipid nanoparticles (LNP).

Methods: This is an interim analysis of a dosage escalation phase 1 study in healthy 18-60-year-old volunteers in Hannover, Munich and Tübingen, Germany, and Ghent, Belgium. After giving 2 intramuscular doses of CVnCoV or placebo 28 days apart we assessed solicited local and systemic adverse events (AE) for 7 days and unsolicited AEs for 28 days after each vaccination. Immunogenicity was measured as enzyme-linked immunosorbent assay (ELISA) IgG antibodies to SARS-CoV‑2 S‑protein and receptor binding domain (RBD), and SARS-CoV‑2 neutralizing titers (MN50).

Results: In 245 volunteers who received 2 CVnCoV vaccinations (2 μg, n = 47, 4 μg, n = 48, 6 μg, n = 46, 8 μg, n = 44, 12 μg, n = 28) or placebo (n = 32) there were no vaccine-related serious AEs. Dosage-dependent increases in frequency and severity of solicited systemic AEs, and to a lesser extent local AEs, were mainly mild or moderate and transient in duration. Dosage-dependent increases in IgG antibodies to S‑protein and RBD and MN50 were evident in all groups 2 weeks after the second dose when 100% (23/23) seroconverted to S‑protein or RBD, and 83% (19/23) seroconverted for MN50 in the 12 μg group. Responses to 12 μg were comparable to those observed in convalescent sera from known COVID-19 patients.

Conclusion: In this study 2 CVnCoV doses were safe, with acceptable reactogenicity and 12 μg dosages elicited levels of immune responses that overlapped those observed in convalescent sera.

Keywords: COVID-19; Dose-response; Neutralizing antibodies; Reactogenicity; S protein.

Publication types

  • Clinical Trial, Phase I
  • Randomized Controlled Trial

MeSH terms

  • Adolescent
  • Adult
  • Antibodies, Viral
  • COVID-19 Vaccines
  • COVID-19* / therapy
  • Double-Blind Method
  • Humans
  • Immunization, Passive
  • Immunogenicity, Vaccine
  • Lipids
  • Middle Aged
  • Nanoparticles*
  • RNA, Messenger
  • SARS-CoV-2
  • Vaccines*
  • Young Adult


  • Antibodies, Viral
  • COVID-19 Vaccines
  • Lipids
  • RNA, Messenger
  • Vaccines

Supplementary concepts

  • COVID-19 serotherapy