RÉSUMÉ
BackgroundThere is an urgent need for fair and equitable access to safe and effective vaccines to end the COVID-19 pandemic. Shortages in reagents and vaccines are a major challenge, as well as limited knowledge on dose response relationship with mRNA COVID-19 vaccines. We explored intradermal fractional dose administration of a mRNA SARS-CoV-2/COVID-19 vaccine as a potential dose-sparing strategy. MethodsWe conducted a proof-of-concept, dose-escalation, open-label, randomised-controlled vaccine trial (IDSCOVA) in healthy adults aged 18-30 years. To test initial safety, ten participants received 10 {micro}g mRNA-1273 vaccine through intradermal injection at day 1 and 29. Following a favourable safety review, thirty participants were 1:1 randomised to receive 20 {micro}g mRNA-1273 either intradermally or intramuscularly. The primary endpoint was tolerability and safety. The secondary endpoint was seroconversion and specific IgG concentration against SARS-CoV-2 spike S1 and Receptor Binding Domain (RBD) after the second dose at day 43. We compared results to two historical cohorts of non-hospitalised COVID-19 patients and vaccinated individuals. FindingsThirty-eight of forty included participants (median age 25 years) completed the study. There were no serious adverse events. Self-reported local adverse reactions after intradermal delivery were mild, both in the 10 {micro}g and the 20 {micro}g group. In the higher dose group, systemic adverse reactions were more common, but still well tolerated. All 38 participants mounted substantially higher IgG-anti-S1 and IgG-anti-RBD concentrations at day 43 than COVID-19 controls. At day 43, anti-S1 (95% CI) was 1,696 (1,309-2,198) BAU/mL for the 10 {micro}g intradermal group, 1,406 (953{middle dot}5-2,074) BAU/mL for the 20 {micro}g intramuscular group and 2,057 (1,421-2,975) BAU/mL for the 20 {micro}g intradermal group. Anti-S1 was 107{middle dot}2 (63-182{middle dot}2) BAU/mL for the convalescent plasma control group and 1,558 (547{middle dot}8-4,433) BAU/mL for the individuals vaccinated with 100 {micro}g mRNA-1273. InterpretationIntradermal administration of 10 {micro}g and 20 {micro}g mRNA-1273 vaccine was well tolerated and safe, and resulted in a robust antibody response. Intradermal vaccination has the potential to be deployed for vaccine dose-sparing. FundingThe trial was supported by crowdfunding (Wake Up to Corona).