Spike makes the first contact with the receptor on the host cell, human angiotensin-converting enzyme 2 (ACE2), and mediates infection by virus–host cell membrane fusion (Hoffmann, Kleine-Weber, Schroeder et al., 2020 ▸; Letko et al., 2020 ▸; Walls et al., 2020 ▸). The gene discussed is ACE2; the disease is infection.