Although ritonavir is a P-gp inhibitor as well, the expressionvariation of P-gp in different tissues likely causes different inhibitionefficacies of PAXLOVID.11 This may explainwhy many patients had COVID-19 rebound after stopping taking PAXLOVIDand SARS-CoV-2 from these patients after COVID rebound did not showresistance to PAXLOVID. Here, PGP is linked to COVID-19.