Fig. 5: Prophylactic efficacy of the pSARS2-S DNA vaccine with or without electrostimulation against SARS-CoV-2 challenge.

Syrian hamsters (n = 6 for vector; n = 8 for 5, 40 Vpp and No EP) were intramuscularly immunized twice at a 3-week interval with 100 μg of vector control, 100 μg of pSARS2-S followed by electrostimulation at the indicated voltage and 120 Hz for 5 s, or 100 μg of pSARS2-S without electrostimulation (No EP). Serum samples were collected at week 6 after the first immunization. At 3 weeks after the final immunization, Syrian hamsters were intranasally challenged with 10⁵ TCID₅₀ SARS-CoV-2. a Spike-specific IgG antibodies were detected by ELISA. b Neutralization titers against wild-type SARS-CoV-2 were examined by neutralization assay. The dashed line indicates the initial fold dilution of serum samples. c Viral titers in the lungs of SARS-CoV-2-infected hamsters at 3 days postchallenge were determined by TCID₅₀ assay. d The body weight change (%) of the hamsters was recorded every day after SARS-CoV-2 challenge. e Histopathology of lungs from infected hamsters at 6 days postchallenge was examined by hematoxylin and eosin staining. Scale bar for the low-magnification image: 1 mm, scale bar for the high-magnification image: 500 μm. f Pathological severity scores of infected hamsters. Neutralization titers are expressed as the geometric mean with a 95% confidence interval, and other data are presented as the mean ± SEM. *p < 0.05, ***p < 0.001 by the Mann–Whitney test.