Fig. 5: Protective immunity in hamsters immunized with SpiN and challenged with SARS-CoV-2.

a The levels of total IgG anti-N and anti-RBD in sera of hamsters vaccinated with SpiN associated to Poly ICLC. b Levels of neutralizing antibodies in the sera from hamsters vaccinated with SpiN + Poly ICLC, in comparison with sera from convalescent individuals. c Viral load measured by RT-PCR in the lungs of control and hamsters immunized with SpiN plus Poly ICLC at 4 days post-infection (dpi) with SARS-CoV-2. Data are presented as mean + /- SEM (b, c). d Histopathological analysis at 2,5x, 5x, and 20x magnification of hamsters at 4 dpi with the Wuhan strain, shows that the lungs in the PBS group display an accentuated diffuse alveolar wall thickening, with moderate multifocal collapse (asterisk), associated with accentuated diffuse congestion (black arrow) and mixed inflammatory infiltrate (mononuclear and polymorphonuclear cells). In the bronchial space, inflammatory cells are noted with a predominance of neutrophils associated with cellular debris (arrowhead) (d, right panels). In comparison, hamsters immunized with SpiN adjuvanted with Poly ICLC had mild focal congestion (black arrow) with alveolar space preservation (d, left panels). a–d Data are representative of two independent experiments. a n = 5 hamsters/group. d PBS n = 3, SpiN + Poly ICLC n = 4, Convalescent n = 3. c Pooled data from two independent experiments, n = 7–8 hamsters/group. Data of viral load quantification was analyzed through two-sided Mann–Whitney test.