Fig. 7: Immunogenicity and protective effect of CVP-containing nasal SARS-CoV-2 S1 vaccine.

Mice received two nasal or intramuscular injections of SARS-CoV-2 S1 alone or S1 with various adjuvants or CVP, with a 4-week interval, followed by euthanasia at various time points post-boost to collect nasal and bronchoalveolar lavage fluids for measuring IgA and IgG antibody levels by ELISA (A and B). Some mice were nasally infected with mouse-adapted SARS-CoV-2 QHmusX virus (from a European lineage) 2 weeks post-boost, and some were euthanized 2 days post-infection to collect lavage fluids for RT–PCR-based viral RNA copy number measurement (C). Body weight changes and survival were monitored for 14 days post-infection (D). Serum collected at 14 days post-boost in (A) was used to measure neutralizing activity against SARS-CoV-2 Wuhan, XBB1.5, and JN.1 variants using a pseudovirus neutralizing assay (E). Lymphocytes isolated from the lungs of mice at 3 days post-boost immunized under the same conditions as in (A) were analyzed by FACS to determine the frequency of germinal center B cells and Tfh cells (F). Each dot represents an individual animal. Bar graphs show the mean values and error bars represent the SEM (A–C, E, and F: n = 5 and C: n = 10) of data from two independent experiments. *p < 0.05, **P < 0.01, ***p < 0.001, and ****p < 0.0001 by Dunnett’s multiple comparison test following the Kruskal–Wallis test (A, B, E, and F: compared with the S1 group and C and D: compared with the non-treated (NT) group). D The log-rank (Mantel–Cox) test was used to compare survival curves (**p < 0.01 compared with the NT group).