ORIGINAL RESEARCH article
Front. Virol.
Sec. Viral Disease Investigation
Distinguishing clinical types and laboratory markers of the ancestral and Omicron variants of COVID-19: A multi-center retrospective study
Xiongwen Tu 1
Huijuan Li 2
Zhenjun Liu 3
Yusheng Cheng 1
Lingling Li 1
1. First Affiliated Hospital of Wannan Medical College, Wuhu, China
2. The Third People's Hospital of Wuhu, Wuhu, China
3. Anqing Hospital of Anhui Medical University, Anqing, China
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Abstract
Objective: Omicron has become a dominant variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) worldwide. A majority of individuals infected with Omicron SARS-CoV-2 infection experience no or mild symptoms but exhibit excessively higher transmissibility than those with infection with the ancestral variant in 2020. This study aimed to identify the distinctive clinical types and laboratory markers of coronavirus disease 2019 (COVID-19). Methods: This retrospective study was performed in multipul medical centers treating patients infected with COVID-19. Demographic characteristics and laboratory data, such as viral shedding time, blood routine test results, and biochemical indicators, were initially recorded after admission. Results: A total of 59 patients with ancestral SARS-CoV-2 infection and 112 patients with Omicron SARS-CoV-2 infection were eventually included. Patients with Omicron SARS-CoV-2 infection were asymptomatic, whereas ancestral variant was common type. Patients with Omicron SARS-CoV-2 infection had markedly higher white blood cell (WBC), eosinophil, and platelet (PLT) counts but remarkably lower lymphocyte counts. The concentration of D-dimer was lower in the Omicron group than in the ancestral variant group. The Omicron variant showed a notably shorter viral shedding time than the ancestral variant, with median durations of 11 and 16 days, respectively (p < 0.001). Multivariate analysis revealed that WBC count, lymphocyte count, eosinopenia, D-dimer, alanine transaminase (ALT), and viral shedding time were independent risk factors for predicting Omicron SARS-CoV-2 infection. Receiver operating characteristic (ROC) curves showed that viral shedding time, ALT, D-dimer and lymphocyte count favored differential diagnosis of ancestral SARS-CoV-2 infection, whereas WBC and eosinophil counts favored the differential diagnosis of Omicron SARS-CoV-2 infection. Conclusions: A majority of the patients infected with Omicron SARS-CoV-2 infection were asymptomatic.WBC count, eosinopenia, and viral shedding time were identified as independent factors for predicting the risk of Omicron SARS-CoV-2 infection. Viral shedding time and eosinophil count were identified as biomarkers for the differential diagnosis of ancestral and Omicron SARS-CoV-2 infections, respectively. Clinical features and various laboratory tests may serve as auxiliary reference indicators to complement viral nucleic acid testing (the diagnostic gold standard) for preliminary stratification of suspected COVID-19 cases, particularly in retrospective analysis of variant-related characteristics.
Summary
Keywords
ancestral, COVID-19, eosinophil, omicron, SARS-CoV-2
Received
29 November 2025
Accepted
17 February 2026
Copyright
© 2026 Tu, Li, Liu, Cheng and Li. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Lingling Li
Disclaimer
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