Figure 5.

Viral load, histopathological changes in vaccinated mice challenged SARS-CoV-2 B.1.1.7 virus. (A) Schema of immunization of aged and young mice through intramuscular injection of COVID-19 mRNA vaccine and virus challenge of vaccinated mice. Young and aged mice were given two doses (5 µg of antigen per mouse) intramuscular injection COVID-19 mRNA vaccine at a 14-day interval, normal saline (NS) as control. Serum samples were taken 14 days after the first injection and again 14 days after the second dose injection. The mice were challenged with 10³PFUs SARS-CoV-2 B.1.1.7 virus 14 days after the second vaccination. Blood and tissue samples were taken on day 2 post virus challenge (2 dpi) for immunology, virological, and histopathological analyses. (B–E) Real-time RT-PCR determined viral RdRp gene copies (B) and infectious virus titre (C) determined by TCID₅₀ assay on Vero E6 cells in the nasal turbinate tissues of infected mice at day 2 post-virus infection. Real-time RT-PCR determined viral RdRp gene copies (D) and infectious virus titre (E) determined by TCID₅₀ assay on Vero E6 cells in the lung tissues of infected mice at day 2 post-virus infection. Data presented as copies of RdRp gene per copy of β-actin in log scale. Data represent mean ± SD. n = 6 for each group. A horizontal dashed line indicates the detection limit of the assays. **P < 0.01, ***P < 0.001, ****P < 0.0001 by Student’s t-test. (F) Representative images of immunofluorescence of viral N protein in the nasal turbinates and lung tissues of vaccinated or NS control young and aged mice at 2 dpi after virus challenge. (G) Representative H&E images of the nasal turbinated and lung tissues of vaccinated or NS control young and aged mice at day 2 post-infection.