Notably, infection by the B.1.617.2 (Delta) variant requires a lower threshold level of ACE2 on the host cell surface, leading to more efficient membrane fusion60; it is therefore highly plausible that B.1.617.2 (Delta) may be able to enter some of the cell lines in this study which B.1.1.7 (Alpha) could not. The gene discussed is ACE2; the disease is infection.