International Rhinologic Society Rhinology 0300-0729 2026 06 04 Comparative analyses of COVID-19-related olfactory dysfunction and classical post-viral olfactory dysfunction: a multicenter retrospective study EN T. Miwa Department of Otorhinolaryngology, Kanazawa Medical University, Kahoku, Ishikawa, Japan K. Tsuzuki Department of Otorhinolaryngology - Head and Neck Surgery, Hyogo Medical University, Nishinomiya, Hyogo, Japan I. Suzaki Department of Otorhinolaryngology Head and Neck Surgery, Showa Medical University, Tokyo, Japan K. Kondo Department of Otorhinolaryngology Head and Neck Surgery, The University of Tokyo, Tokyo, Japan E. Mori Department of Otorhinolaryngology, The Jikei University School of Medicine, Tokyo, Japan M. Kobayashi Department of Otorhinolaryngology-Head and Neck Surgery, Mie University Graduate School of Medicine, Tsu, Mie, Japan M. Suzuki Department of Otorhinolaryngology-Head and Neck Surgery, Nagoya City University, Nagoya, Aichi, Japan K. Fushimi Department of Otorhinolaryngology, Kobe Century Memorial Hospital, Kobe, Hyogo, Japan T. Saito Department of Otorhinolaryngology - Head and Neck Surgery, Hyogo Medical University, Nishinomiya, Hyogo, Japan T. Hirose Department of Otorhinolaryngology - Head and Neck Surgery, Hyogo Medical University, Nishinomiya, Hyogo, Japan H. Shiga Department of Otorhinolaryngology, Kanazawa Medical University, Kahoku, Ishikawa, Japan M. Takeuchi Department of Otorhinolaryngology Head and Neck Surgery, Showa Medical University, Tokyo, Japan N. Okuzawa Department of Otorhinolaryngology Head and Neck Surgery, Showa Medical University, Tokyo, Japan K. Ogawa Department of Otorhinolaryngology Head and Neck Surgery, The University of Tokyo, Tokyo, Japan R. Sekine Department of Otorhinolaryngology, The Jikei University School of Medicine, Tokyo, Japan M. Nagai Department of Otorhinolaryngology, The Jikei University School of Medicine, Tokyo, Japan M. Tei Department of Otorhinolaryngology, The Jikei University School of Medicine, Tokyo, Japan H. Tanaka Department of Otorhinolaryngology, The Jikei University School of Medicine, Tokyo, Japan Y. Kishimoto Department of Otorhinolaryngology, The Jikei University School of Medicine, Tokyo, Japan H. Morishita Department of Otorhinolaryngology-Head and Neck Surgery, Mie University Graduate School of Medicine, Tsu, Mie, Japan E. Ishigami Department of Otorhinolaryngology-Head and Neck Surgery, Mie University Graduate School of Medicine, Tsu, Mie, Japan H. Nakanishi Department of Otorhinolaryngology-Head and Neck Surgery, Nagoya City University, Nagoya, Aichi, Japan R. UehaDepartment of Otorhinolaryngology Head and Neck Surgery, The University of Tokyo, Tokyo, Japan Swallowing Center, the University of Tokyo Hospital, Tokyo, Japan Y. Iinuma Department of Infectious Diseases, Kanazawa Medical University, Kahoku, Ishikawa, Japan Y. Iida Department of Mathematics, Kanazawa Medical University, Kahoku, Ishikawa, Japan Journal Article 3434 10.4193/Rhin25.396 INTRODUCTION: Olfactory dysfunction (OD) is a common symptom of COVID-19. However, prevalence and clinical characteristics of OD due to COVID-19 (COVID-19-OD) differ from those of conventional post-viral OD (PVOD). Even among COVID-19-OD cases, they vary depending on the virus subtype. We aimed to compare the differences between COVID-19-OD and PVOD, as well as the differences across viral variants within COVID-19-OD. METHODS: This is a multicenter retrospective study. The subjects were PVOD patients from 2017 to 2019 and COVID-19-OD patients from 2020 to 2022. Patient backgrounds, olfactory cleft condition, and olfactory function were obtained from medical records and compared. RESULTS: Of the 649 patients, 269 had COVID-19-OD (pre-Omicron: 191; Omicron: 78) and 380 had PVOD. Compared to the PVOD group, the COVID-19-OD group was younger and exhibited a higher rate of olfactory cleft obstruction and a greater prevalence of parosmia or phantosmia. The severity of OD was milder in the COVID-19-OD group. Even after controlling for age, the severity of OD remained milder in the COVID-19-OD group. Compared to the Omicron group, the pre-Omicron group was younger and had a higher incidence of parosmia or phantosmia. CONCLUSION: COVID-19-OD and PVOD differ significantly in clinical features and in the pathophysiology of OD. Moreover, even within COVID-19-OD, there are differences between the variants, which are thought to reflect biological differences in the virus.