Level of anti-RBD IgG and in vitro neutralization of spike variants following SARS-CoV-2 mRNA vaccination. (A) Presents anti-RBD IgG antibody concentration prior to vaccination (prevax), after dose 1 (mean = 18.5 days), after dose 2 (mean = 20.7 days), and 3 months after dose 1 (mean = 95.5 days) for 27 participants. Lines connect results for individual participants, median value is shown with a dotted line, and dot color indicates history of SARS-CoV-2 exposure prior to vaccination (PCR positive confirmed COVID-19, seropositive but asymptomatic, and seronegative). Wilcoxon matched pairs signed-rank tests were used to evaluate statistical significance of median differences. Overall, antibody concentration was significantly lower at 3 months than after dose 2 (p < 0.0001). (B) Presents inhibition of spike-ACE2 receptor binding using a surrogate virus neutralization test that measures inhibition of wild-type (Wuhan) spike, as well as the P.1, B.1.351, and B.1.1.7 variants. In comparison with wild-type, neutralization of all variants was significantly lower following dose 1, dose 2, and at 3 months (all comparisons p < 0.0001). Neutralization of each variant was significantly lower at 3 months than after dose 2 (all comparisons p < 0.001). (C) Predicts anti-RBD IgG at 3 months as a function of dose 2 response. Regression analysis indicates that the dose 2 response is a strong predictor of the 3 month response (R2 = 0.839 (p < 0.0001). A second order in dose 2 showed evidence of a non-linear trend (R2 = 0.898; analysis of variance for the nested model p = 0.0023). (D) Presents neutralization of each variant at 3 months post-vaccination by SARS-CoV-2 exposure history. Wilcoxon rank-sum test was used to evaluate statistical significance of differences by exposure history. Neutralization of spike-ACE2 interaction did not differ between seropositive and seronegative participants for any variant (all comparisons p > 0.2). Neutralization against all the variants was higher for PCR positive cases in comparison with seropositive and seronegative participants.