RESUMEN
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-CoV2 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-CoV2 Sprotein and receptor binding domain (RBD), and SARS-CoV2 neutralizing titers (MN50). RESULTS: In 245 volunteers who received 2 CVnCoV vaccinations (2⯵g, nâ¯= 47, 4⯵g, nâ¯= 48, 6⯵g, nâ¯= 46, 8⯵g, nâ¯= 44, 12⯵g, nâ¯= 28) or placebo (nâ¯= 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 Sprotein and RBD and MN50 were evident in all groups 2 weeks after the second dose when 100% (23/23) seroconverted to Sprotein or RBD, and 83% (19/23) seroconverted for MN50 in the 12⯵g group. Responses to 12⯵g 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⯵g dosages elicited levels of immune responses that overlapped those observed in convalescent sera.