XK and COVID-19: However, the 3′–5′ exonuclease (ExoN) of SARS-CoV-2 may limit the antiviral effects of NA inhibitors incorporated into nascent RNA.3 To date, some NAs which can evade the ExoN proofreading function have shown potent anti-coronavirus activity in preclinical studies and have entered clinical trials for COVID-19 treatment, among which molnupiravir was just approved by Australia on August 9, 2021, for treating COVID-19.