Fig. 7. Immune responses and protection after a single immunization.

a Immunization and challenge schedule for IFNAR^−/− mice (n = 6). Animals were immunized interperitoneally on day 0. Sera were collected at days 24 and 48. Animals were challenged on day 48 by intranasal inoculation of mouse-adapted SARS-CoV-2 virus (MACo3) at 1.5 × 10⁵ PFU. Sera were assessed for levels of specific antibodies to b MV and c S-SARS-CoV-2 protein. d Neutralizing antibody responses against SARS-CoV-2 virus, expressed as 50% plaque reduction neutralization test (PRNT₅₀) titers. e SARS-CoV-2 viral RNA copies detected by RT-qPCR in homogenized lungs of challenged animals, calculated as copies/lung. f Titer of infectious viral particles recovered from the homogenized lung of the immunized animals expressed as PFU/lung. Dotted blue line indicates the limit of detection (LOD). Data are represented as geometric means with line and error bars indicating ±geometric SD. Statistical significance was determined by b–d two-way ANOVA with Tukey’s multiple comparisons test, e–g Kruskal–Wallis one-way ANOVA test with Dunn’s multiple comparison test.