Figure 4. The boosting side of SARS-CoV-2 mRNA vaccine impacts the affinity and breadth of antibody response.

Mice were primed with 0.2 μg SARS-CoV-2 mRNA vaccine and boosted 3 weeks later either in the ipsilateral or the contralateral limb. Serum samples collected 9 days and 19 weeks post booster vaccination were analyzed by ELISA and affinity-ELISA for binding titer and affinity of antibodies, respectively.

(A) SARS-CoV-2 RBD-and spike-specific IgG binding titer measured by ELISA.

(B) Antibody affinity of samples from (A) as measured by IC₅₀ using affinity-ELISA.

(C and D) Samples from (A) were tested for the cross-reactivity against RBD and spike proteins from Omicron viral variant. Binding titer is shown in (C), and affinity is shown in (D). n = 9–10 for day 9 post boost groups from two independent experiments; n = 11–13 for week 19 post boost groups from three independent experiments. Each dot represents one mouse, with lines depicting the median. Data were analyzed by unpaired t test. *p < 0.05; ****p < 0.0001; ns: not significant.