Fig. 4: The effect of stimulation frequency and time on SARS-CoV-2-infected hamsters.
a–d Syrian hamsters (n = 8 per group) were intramuscularly immunized three times at a 2-week interval with 100 μg of vector control or pSARS2-S, followed by electrostimulation at 40 Vpp with a frequency of 50 or 120 Hz for 10 s. e–h Hamsters (n = 8 per group) received 40 Vpp/120 Hz electrostimulation for 3 or 5 s following DNA injection, and three-dose vaccination regimen was described as above. Serum samples obtained at week 6 after the first immunization were used in this experiment. a, e Endpoint titers of serum IgG specific to spike protein were evaluated by ELISA. b, f Serum neutralizing activity against wild-type SARS-CoV-2 was evaluated by neutralization assay. The dashed line indicates the initial fold dilution of serum samples. At 3 weeks after the final immunization, Syrian hamsters were intranasally challenged with 105 TCID50 SARS-CoV-2. c, g Viral titers in the lungs of SARS-CoV-2-infected hamsters at 3 days postchallenge were determined by TCID50 assay. d, h Body weight change (%) of the hamsters was recorded every day after SARS-CoV-2 challenge. 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.
