Figure 2.

Booster shot of mRNA vaccine in non-infected individuals generates hybrid immunity-like benefits 1 month after last immunization

(A) Schematic representation of plasma samples collection from individuals previously infected or not, who received 2 or 3 doses of mRNA vaccine were tested for neutralization activity against pseudo viruses expressing the WH1, B.1.217.2 (Delta), BA.1, BA.2, and BA.4/5 SARS-CoV-2 Spike proteins. Plasma samples were collected at about 1 month after last vaccination.

(B) Raw ID₅₀ (reciprocal dilutions) titers against the indicated variant Spikes. Horizontal bars and numbers indicate ID₅₀ geometric means (GMT) for each group and error bars indicate 95% confidence intervals. At the bottom are fold changes for the indicated comparisons. Significant p values are indicated for comparisons between all groups (Kruskal-Wallis test with two-stage step-up multiple comparison, ∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.001, ∗∗∗∗p < 0.0001). Dashed lines indicate the assay lower limit of detection (60 reciprocal dilutions). Non-responder rate was defined by undetectable neutralization titers for a specific variant at an initial serum dilution of 1:60 and are indicated. Participants (3 from the +/3/− group) who only received 1 dose as part of the full vaccine schedule are indicated in blue.

(C) Ratio of WH1 ID₅₀ over the indicated VOC ID₅₀ calculated for the groups with plasma samples at 1 month (shown in 2A) after last vaccine dose. Horizontal bars indicate ratio geometric means for each group and error bars indicate 95% confidence intervals. Bottom numbers indicate fold reduction compared to WH1. Significant p values are indicated for comparisons between all groups (Kruskal-Wallis test with two-stage step-up multiple comparison, ∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.001, ∗∗∗∗p < 0.0001). Non-responder samples are indicated by an open circle. Participants (3 from the +/3/− group) who only received 1 dose as part of the full vaccine schedule are indicated in blue. See also Figures S3 and S4.