Neutralization titers against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants. The monoclonal antibody (mAb) solutions (A) and serum samples from (B) convalescent or (C) vaccinated individuals were serially diluted (1:2) and incubated with 4000 TCID₅₀ (median tissue culture infective dose)/mL of the indicated SARS-CoV-2 variant. Susceptible cells were subsequently inoculated and analyzed for a cytopathic effect formation after 72-hour incubation. Values represent reciprocal dilutions of SARS-CoV-2 microneutralization titers resulting in 50% virus neutralization (NT₅₀). The indicated mAb solutions were used in physiological concentrations according to the manufacturer’s instructions (Regeneron Pharmaceuticals and Eli Lilly and Company, respectively). Mean values from 2 replicates are shown, each determined with Caco2 and A549-AT cells. Colored dots represent serum samples from individuals vaccinated with messenger RNA 1273 (red) or BNT162b2 (blue). Statistical significance, compared with SARS-CoV2 B (FFM1) or B.1 (FFM7), respectively, was determined using a 1-tailed, paired Student t test; sample 21 (from an individual vaccinated with BNT162b2 after convalescence) was excluded from statistical analysis. Control serum samples were tested negative for SARS-CoV-2 antibodies. *P < .05); **P ≤ .01; NS, not significant.