BNT162b1 is a nucleoside-modified mRNA vaccine formulated with lipid nanoparticles that encode the trimerized receptor-binding domain (RBD) of the SARS-CoV-2 peak glycoprotein. This article reports the safety, tolerability, and immunogenicity data obtained from an ongoing placebo-control, dose-escalation, and observer-blind study that included 45 healthy adults (18-55 years), randomized to receive 2 doses, separated by 21 days, 10 µg, 30 µg or 100 µg of BNT162b1. Local reactions and systemic events to the vaccine were found to be dose-dependent, mostly mild or moderate, and transient. A second 100 μg dose was not administered due to increased reactogenicity and lack of significant increase in immunogenicity compared to the first 30 μg dose. RBD-binding IgG concentrations and SARS-CoV-2 neutralizing titers in serum increased with the first and second doses. The geometric mean of neutralizing titers was 1.9 to 4.6 times higher than a panel of COVID-19 convalescent human sera, obtained 14 days after a positive PCR for SARS-CoV-2. These results support further evaluation of this mRNA vaccine candidate. However, the limitations of this study include the lack of time to follow-up the participants (it will continue for at least 6 months), in addition to the lack of inclusion of a population at high risk for severe disease due to COVID-19.