The COVID-19 pandemic continues to be a public health threat. Multiple mutations in the spike protein of emerging variants of SARS-CoV-2 appear to impact on the effectiveness of available vaccines. Specific antiviral agents are keenly anticipated but their efficacy may also be compromised in emerging variants. One of the most attractive coronaviral drug targets is the main protease (Mpro). A promising Mpro inhibitor of clinical relevance is the peptidomimetic PF-07321332. We expressed Mpro of

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... ve SARS-CoV-2 lineages (C.37 Lambda, B.1.1.318, B.1.2, B.1.351 Beta, P.2 Zeta), each of which carries a strongly prevalent missense mutation (G15S, T21I, L89F, K90R, L205V). Enzyme kinetics showed that these Mpro variants are similarly catalytically competent as the wildtype. We show that PF-07321332 has similar potency against the variants as against the wildtype. Our in vitro data suggest that the efficacy of specific Mpro inhibitors such as PF-07321332 is not compromised in current COVID-19 variants.