ACE2 and infection: The human ACE2 transgenic C57BL/6 mouse model was used for the challenge assay, revealing unchanged weight and no clinical sign in the vaccinated mice after infection with original type SARS-CoV-2, while mice that received placebo showed an increased clinical score and a significant decrease in weight after infection.101 The assessment of the viral load revealed no detectable SARS-CoV-2 RNA in both lungs of the vaccinated mice compared to the mice treated with a placebo.