The emergence of SARS-CoV-2 has resulted in >90,000 infections and >3,000 deaths. Coronavirus spike (S) glycoproteins promote entry into cells and are the main target of antibodies. SARS-CoV-2 spike uses ACE2 to enter cells and that the receptor-binding domains of SARS-CoV-2 spike and SARS-CoV spike bind with similar affinities to human ACE2, correlating with the efficient spread of SARS-CoV-2 among humans.