3.2. Animals

Syrian hamsters are the optimal model for studying vaccines against COVID-19. According to Rosenke et al. (2020), the sex of animals does not play a significant role in the severity of SARS-CoV-2 infection [5]. In contrast, in a more recent study performed by Dhakal et al. differences in the course of SARS-CoV-2 infection in male and female hamsters were reported [6]. Sex differences in COVID-19 outcomes in humans are also described [7,8]. Therefore, there is a limitation of our study due to the fact that it was performed only on female Syrian hamsters. The golden Syrian hamsters (Mesocricetus auratus) (female; weight of 40–45 g) obtained from the Branch of the Shemyakin–Ovchinnikov Institute of Bioorganic Chemistry of the Russian Academy of Sciences (Nursery for the Laboratory Animals, Pushchino, Russia) were used.