Fig. 6: Heterologous boosting with Gamma RBD-adapted vaccine formulation of different primary vaccine platforms.

a Immunization protocol scheme. BALB/c mice were immunized at day 0 and day 21 via i.m. with: Gamma RBD + Alum (blue), BNT162b2 (red), BBIBP-CorV (green) and ChAdOx1-S (violet). At day 100 (M3) half of mice received homologous third doses (BNT162b2, BBIBP-CorV or ChAdOx1-S accordingly to table in panel a and the other half of mice received heterologous booster shots with Gamma RBD + Alum. b Ancestral RBD-specific IgG titers in sera of immunized animals at day 98 post prime immunization. Bars are GMT ± 95% CI. Gamma RBD + Alum (n = 5 mice, blue), BNT162b2 (n = 10 mice, red), BBIBP-CorV (n = 10 mice, green) and ChAdOx1-S (n = 10 mice, violet). Kruskal Wallis test. *p < 0.05, **p < 0.01, ***p < 0.001. Exact p values are shown. c Comparison of RBD-specific IgG titers pre and post-boost immunization. Numbers in bold are GMT fold-increase values. Bars are GMT ± 95% CI. n = 5 mice per group. Kruskal Wallis. *p < 0.05. Exact p values are shown. d Neutralizing-antibody titers against Ancestral and Gamma SARS-CoV-2 were evaluated pre (98 dpp) and post boost immunization (121 dpp) of mice. Neutralization titer was defined as the serum dilution that reduces 50% of the cytopathic effect (NT50). Bars are GMT ± SD. Numbers in bold are fold-increase of GMT values for each group. n = 5 mice per group. One-way ANOVA and Bonferroni multiple comparison test. *p < 0.05, **p < 0.01, ***p < 0.001. Exact p values are shown. e Neutralizing activity of antibodies against Omicron (BA.1 and BA.5) were evaluated 21 days post boost immunization of mice. Neutralization titer was defined as the serum dilution that reduces 50% the cytopathic effect (NT50). Bars are GMT ± SD and numbers are GMT values for each group of mice. n = 5 mice per group. Kruskal Wallis test. **p < 0.01, ***p < 0.001. Exact p values are shown Source data are provided as a Source Data file.