Nirmatrelvir-resistant SARS-CoV-2 is efficiently transmitted in Syrian hamsters

The SARS-CoV-2 main protease (3CLpro) is one of the promising therapeutic target for the treatment of COVID-19. Nirmatrelvir is the only the 3CLpro inhibitor authorized for treatment of COVID-19 patients at high risk of hospitalization; other 3Lpro inhibitors are in development. We recently repored on the in vitro selection of a SARS-CoV2 3CLpro (L50F-E166A-L167F; short 3CLprores) virus that is cross-resistant with nirmatrelvir and yet other 3CLpro inhibitors. Here, we demonstrate that the resistant virus replicates efficiently in the lungs of intranassaly infected hamsters and that it causes a lung pathology that is comparable to that caused by the WT virus. Moreover, 3CLprores infected hamsters transmit the virus efficiently to co-housed non-infected contact hamsters. Fortunately, resistance to Nirmatrelvir does not readily develop (in the clinical setting) since the drug has a relatively high barrier to resistance. Yet, as we demonstrate, in case resistant viruses emerge, they may easily spread and impact therapeutic options for others. Therefore, the use of SARS-CoV-2 3CLpro protease inhibitors in combinations with drugs that have a different mechanism of action, may be considered to avoid the development of drug-resistant viruses in the future.