TMPRSS2 and infection: We further incorporated Delta + T95I and Delta + T95I + P812S in the panel because P812S was predominantly found in Delta (AY.4), and a previous genomic-epidemiological study showed that P812S21 further increases the likelihood of Delta breakthrough infections.29,30 We then performed infectivity assays using pseudoviruses with and without the P812S mutations on cell lines that varied in ACE2 and TMPRSS2 expression levels (Figures S5B–S5E).