ACE2 and infection: To address this, we employed a pseudovirus system—a replication-deficient viral model engineered to express the SARS-CoV-2 spike protein—aimed to assess infection efficiency using the Omicron variant pseudovirus in a stable HEK-293 cell line expressing human ACE2 (HEK293/ACE2), in the presence of bromhexine hydrochloride.