Fig. 5: SARS-CoV-2 spike variant neutralizing antibodies induced by Ad26.COV2.S.529 in pre-immune hamsters 23 weeks after pre-exposure.

Hamsters with pre-existing immunity were generated by pre-vaccination with 10⁷ viral particles (vp) of Ad26NCOV006 (Ad26 vector encoding Wuhan-Hu-1 spike, pre-immune animals) at week −27. Naive control hamsters were not vaccinated (NA). At week −4, Ad26 Wuhan-Hu-1 spike-vaccinated hamsters were vaccinated with 10⁹ vp Ad26.COV2.S (S), Ad26.COV2.S.529 (529), a 1:1 combination of S and 529 or Ad26.Empty (all n = 13–14). In addition, naive hamsters were vaccinated with Ad26.Empty (n = 14). Serum was collected at week 0 for psVNA analysis. Neutralizing antibody titers are expressed as the dilution giving a 50% reduction (N₅₀) in the normalized luciferase readout (normalization relative to control wells without any serum added). Horizontal red bars and values per vaccination group represent geometric mean (GMT) titers. Dashed horizontal lines represent the lower limit of detection (LLOD). Open symbols indicate the response is at or below the LLOD. Comparisons to the pre-vaccinated Ad26.Empty group and pairwise comparisons were performed by a t test, Tobit Z test, or Mann–Whitney test with a threefold Bonferroni correction. Significance is shown compared with the pre-vaccinated-only group unless depicted otherwise. Statistical differences are indicated by asterisks: **P < 0.01, ***P < 0.001.