ACE2 and coinfection: Although we found that H5N1 induced higher levels of the ACE2 receptor (long form of ACE2) than SARS-CoV-2 infection alone, we did not observe an enhancement in the SARS-CoV-2 viral titers upon co-infection with H5N1 in the alveolar epithelial cells (Figure 3c and Figure S2c).