Fig. 2. Increased breadth after the heterologous boost immunization.

A Study design and sampling schedule. Animals were immunized with NVX-CoV2373 at weeks 0 and 4 and boosted with NVX-CoV2443 at week 35. WA-1 Spike structure was obtained from PBD ID J771, with mutations in P.1 Spike compared to WA-1 Spike labeled in red. B IgG plasma binding titers to WA-1 Spike and RBD (n = 6). C Serum neutralization of WA-1/2020 SARS-CoV-2 virus (n = 6). Gray shaded area represents the NT50 of WHO international standard NIBSC 20/136 (WHO IS). D Serum neutralization using WA-1 Spike pseudotyped VSV virus particles (n = 6). E Frequency of WA-1 Spike-specific bone marrow plasma cells (BMPC) (n = 6). Representative ELISpot wells are shown on the left. All data is background subtracted based on OVA wells. F IgG binding antibodies in BAL (n = 4–6. Samples with total IgG endpoint titer <1000 were excluded from analysis). PP = pre-pandemic BAL samples. G, H Cross-reactive serum antibodies to WA-1 and P.1 Spike protein (n = 6). IgG binding titers to WA-1 Spike with and without depletion by P.1 Spike (G) and proportion of depleted antibodies (H). Serum neutralization of pseudotyped VSV viruses carrying variant Spike proteins (P.1, Omicron BA.2 and BA.5) at different timepoints (I) and the ratios between neutralization of the variants compared to WA-1 (J) (n = 6). NN = not neutralizing. Data is presented as geometric mean ± geometric SD (B–F, I, J) or mean ± SEM (H). Statistical analysis was performed using Wilcoxon test (H) and repeated measures two-way ANOVA with the Geisser-Greenhouse correction and Tukey’s multiple comparisons test (I). Dose 1, dose 2, and dose 3 refer to 2 weeks after each immunization. Dotted line represents lower level of detection (B, D–G, I) or the ratio of 1 (J). LLOD lower level of detection, ULOD upper level of detection.