The spike (S) protein on SARS-CoV-2 virions is a promising candidate for a vaccine as it is: 1) indispensable for viral entry into the host cells through binding to angiotensin-converting enzyme 2 (ACE2) expressed on the host cells, and 2) the major target of virus neutralizing antibodies in patients who recover from COVID-19. This evidence concerns the gene ACE2 and COVID-19.