Violin plots of circulating SARS-CoV-2 anti–spike protein receptor-binding domain antibodies in serum samples obtained from participants after they received 2 doses of an mRNA vaccine. Inside each violin plot, the geometric mean is depicted as a point. A, Difference between participants vaccinated with mRNA-1273 (Moderna) vs those with BNT162b2 (Pfizer-BioNTech). B, Difference according to previous SARS-CoV-2 infection and the type of mRNA vaccine. C, Difference according to age and the type of mRNA vaccine in previously uninfected participants. All comparisons were significant at P < .001 except previously infected participants (panel B), which was significant at P = .01.