Association between sore throat and early immune responses against COVID-19 before and after the emergence of the Omicron variant

Background: Sore throat is a prevalent symptom of coronavirus disease 2019 (COVID-19), particularly when caused by the Omicron variants. However, the association between sore throat and immune responses to different severe acute respiratory syndrome coronavirus 2 variants remains unclear. This study aimed to elucidate the characteristics of immune responses associated with sore throat in patients with COVID-19 before and after the emergence of Omicron.

Methods: In this prospective observational study, we enrolled patients with COVID-19 hospitalized between December 2020 and April 2022, which covered the pre-Omicron and Omicron (BA.1 variant) endemic periods. Sore throat was assessed using a daily questionnaire, including an analog scale for sore throat grade (0 to 3) from admission until discharge. Serum levels of immune indicators were assessed using enzyme-linked immunosorbent assay.

Results: A total of 47 patients infected with Omicron and 136 patients infected with preceding variants were included in the analyses. The frequency of sore throat was significantly higher in participants infected with Omicron than that in those infected with preceding variants (66% vs. 42%, P<0.005). Sore throat was associated with nasopharyngeal viral load, interleukin-6 (IL-6)/interferon-α (IFN-α) levels in participants infected with preceding variants, whereas, it was associated with age, the body mass index, and interferon-λ1 (IFN-λ1) in participants infected with Omicron.

Conclusions: Infection with the Omicron variant is characterized by increased sore throat frequency and altered associations between sore throat and several immune indicators, including IFN-α, IL-6, and IFN-λ1.