Ensitrelvir suppresses prolonged olfactory abnormalities derived from SARS-CoV-2 infection in hamsters

Ensitrelvir, an oral severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) 3CL protease inhibitor, is reportedly effective in suppressing smell disorder onset, a post-coronavirus disease 2019 (COVID-19) condition symptom. However, the pathogenesis of post-COVID-19 condition symptoms and the mechanism underlying the onset-suppressive effect of ensitrelvir are not fully understood. Here, we explored a post-COVID-19 condition model in hamsters 1 month post-SARS-CoV-2 infection and showed that ensitrelvir treatment caused early recovery of body weight, viral RNA suppression, and sense of smell improvement. In the nasal turbinates, SARS-CoV-2 was associated with significantly increased inflammatory markers, many of which were suppressed by ensitrelvir. Significant positive correlations were observed between smell testing and many inflammation-related markers in the nasal turbinates. In conclusion, our study indicates that chronic inflammation may occur in the nasal turbinates over a long period post-SARS-CoV-2 infection, leading to smell disorder onset in a hamster model. Early ensitrelvir treatment post-infection suppressed inflammation in the nasal turbinates and prevented smell disorder onset.