Changes in Clinical Features and Severity of COVID-19 with the Emergence of Omicron Variants: A Shift Towards a Common Disease

Saori Kawamura,1,* Fumihiro Yamaguchi,1,* Rui Kusakado,1 Yoshihiro Go,1 Shiho Nohmi,1 Chinatsu Yoshizaki,1 Yuki Yoshida,1 Kensuke Izumizaki,1 Yuichiro Saito,1 Hitoshi Kobayashi,1 Kento Hirata,1 Kenta Miyo,1 Chika Kondo,1 Mamiko Kanzaki,1 Yize Ding,1 Takuya Yokoe,1 Sei Kobayashi,2 Hiroshi Suzuki3 1Department of Respiratory Medicine, Showa University Fujigaoka Hospital, Yokohama, Japan; 2Department of Otolaryngology, Showa University Fujigaoka Hospital, Yokohama, Japan; 3Department of Cardiovascular Medicine, Showa University Fujigaoka Hospital, Yokohama, Japan*These authors contributed equally to this workCorrespondence: Saori Kawamura, Department of Respiratory Medicine, Showa University Fujigaoka Hospital, 1-30 Fujigaoka, Aoba-ku, Yokohama, 227-8501, Japan, Tel +81-45-971-1151, Email [email protected]: The emergence of the Omicron variant of severe acute respiratory syndrome coronavirus-2 has significantly altered the clinical features and severity of coronavirus disease 2019 (COVID-19).Objective: This study aims to evaluate whether the clinical factors that previously predicted COVID-19 remain valid following the emergence of the Omicron variant.Methods: This cross-sectional study was conducted at Showa University Fujigaoka Hospital from April 2022 to March 2023. A total of 576 patients with suspected COVID-19 were included, of which 258 (44.8%) were diagnosed with COVID-19 based on real-time reverse-transcription polymerase chain reaction tests. Clinical data were collected retrospectively, and multivariate logistic regression was used to analyze factors associated with a COVID-19 diagnosis.Results: Of the 258 patients diagnosed with COVID-19, 60% had mild disease, and the overall severity was lower than in previous reports prior to the emergence of the Omicron variant. In the multivariate analysis, only C-reactive protein (CRP) levels were significantly associated with COVID-19 (odds ratio, 0.3164; 95% confidence interval, 0.2077– 0.4819), while factors such as age, sex, body mass index, lactate dehydrogenase, and comorbidities were not significantly associated. Non-COVID-19 cases were primarily bacterial infections, accounting for 57.2% of the non-COVID-19 diagnoses. Mortality rates did not differ significantly between the COVID-19 and non-COVID-19 groups.Conclusion: The clinical characteristics of COVID-19 have become less distinct since the emergence of the Omicron variant, with CRP being the primary marker associated with a COVID-19 diagnosis. As COVID-19 continues to transition towards a more common infectious disease, distinguishing it will become increasingly challenging.Keywords: severe acute respiratory syndrome coronavirus-2, coronavirus disease 2019, Omicron variants, C-reactive protein