Methods
RBD, beta variant RBD
ADVERSE EVENTS
We conducted a phase 1, randomised, double-blind, placebo-controlled, dose-escalation study to determine the safety and immunogenicity of single booster doses of a SARS-CoV-2 beta variant RBD recombinant protein vaccine adjuvanted with MF59® (Seqirus, Inc) (Protein-RBD), and a SARS-CoV-2 beta variant membrane-anchored RBD mRNA vaccine encapsulated within lipid nanoparticles (mRNA-RBD). The principal endpoints related to safety were serious adverse events (SAEs, Day 1–29), medically attended adverse events (MAAEs) and any adverse events (AEs) leading to study withdrawal at any time during the study, solicited local and systemic reactogenicity within 7 days after vaccination, and unsolicited AEs from Day 1 to Day 29, and to immunogenicity as measured by SARS-CoV-2 neutralising or RBD-specific antibody titres compared to baseline. Proportion of subjects with 4-fold or greater post-vaccination antibody responses was initially conceived as a principal outcome for a priming 2-dose series in non-immune (vaccine naïve and previously uninfected) participants, but this was considered inappropriate for a 4th dose booster criterion.