Prevalence of Low-Frequency, Antiviral Resistance Variants in SARS-CoV-2 Isolates in Ontario, Canada, 2020-23

The study evaluated over 78,000 SARS-CoV-2 genomes, looking for the development of resistance mutations to a newly approved oral antiviral against SARS-CoV-2, called Nirmatrelvir-ritonavir. The team looked for specific mutations in the main viral protease encoded by nsp5, which confers resistance to Nirmatrelvir-ritonavir. Mutations in the nsp5 gene were found in a small number of SARS-CoV-2 isolates in Ontario (0.16%), but it was unclear if these mutations were due to antiviral pressure or random mutations because of viral replication. These findings suggest that significant resistance to Nirmatrelvir-ritonavir has not developed yet, but with increased clinical use, continued surveillance for anti-viral resistance variants is important to inform clinical practice, vaccine development and public health policy.

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