Analysis of influenza epidemics in northern China during 2018-2021 and exploration of early diagnosis on influenza B (preprint)

ABSTRACT

Background: Research on the impacts of COVID-19 towards influenza and the early diagnosis of influenza B is limited. This study aimed to analyze the impacts of COVID-19 pandemic on influenza epidemics in northern China and explore the early-diagnosis indicators of influenza B. Methods: 1. Data of influenza-like illness (ILI) and influenza virological surveillance in northern China during 2018-2021 winter influenza season were collected to analyze the impacts of COVID-19 pandemic on influenza epidemics.  2. Clinical characteristics of 38 influenza B positive patients and 38 influenza B negative patients confirmed during 2021 winter influenza season were retrospectively observed. Clinical symptoms and blood routine indicators of both groups were compared and analyzed. Results: 1. During 2020 and 2021 winter influenza season, ILI% and influenza virus positive rate in northern China were both lower than those in 2018 and 2019, with the influenza B (Victoria) dominating.  2. Compared with influenza B negative group, the systemic symptoms in influenza B positive group were significantly increased. The value of white blood cell, neutrophils%, C-reactive protein and serum amyloid A in influenza B positive group were significantly lower than those in negative group, while the lymphocytes% and monocytes% were higher than those in negative group and both could be regarded as the diagnostic indicators of influenza B. Conclusions: Influenza epidemics were greatly reduced during COVID-19 pandemic, with influenza B rebounding from 2021, and continuous surveillance is still needed. Both clinical features and blood routine indicators can be helpful towards the early diagnosis on influenza B.