2.9  Statistical analysis
GraphPad Prism 7 software (GraphPad Software Inc., La Jolla, CA, USA) was used for the statistical analyses. For the antibody test, growth kinetics, tissue tropism, and viral shedding test, the collected data were analyzed using a two-way ANOVA to determine whether there was a significant difference between the different groups. The significance was considered as follows: significant at P ≤ 0.05 (*); highly significant at P ≤ 0.01 (**); and extremely significant at P ≤ 0.001 (***).