“…Furthermore, numerous pieces of evidence show that SARS-CoV-2 infection has occurred in humans for a long time or even years ago. A recent report showed the spike protein receptor binding domain (RBD) may have a high affinity for human cell targets at least since 2013[ 34 ]. Besides, the vaccine is the best way to prevent and control virus infection, however, although several candidate vaccines have been applied in clinical trials, the efficacy and safety of these vaccines still need further evaluation.…”