Impact of coronavirus disease 2019 nonpharmaceutical interventions on influenza epidemiology: A retrospective analysis in Hebei Province, China from 2019 to 2023.

BackgroundIn this study we retrospectively analyzed the influenza virus antigen detection data from Hebei General Hospital for the period from 2019 to 2023, focusing on the impact of coronavirus disease 2019 nonpharmaceutical interventions on the epidemiology of influenza.MethodsA retrospective analysis was conducted on 45,956 records of patients with influenza-like illness retrieved from the Laboratory Information System of Hebei General Hospital between January 2019 and December 2023. Nasal and pharyngeal swab samples from these patients were tested for influenza A and influenza B virus antigens using colloidal gold immunochromatographic assay.ResultsCompared with the pre-pandemic period, both number of influenza cases and positive detection rates declined substantially during the coronavirus disease 2019 pandemic. Notably, this decline coincided with the peak implementation of nonpharmaceutical interventions aimed at mitigating coronavirus disease 2019 spread. The cases of influenza surged significantly following the relaxation of coronavirus disease 2019 restrictions in 2023 and even approached or exceeded the pre-coronavirus disease 2019 levels.ConclusionsOur findings provide strong evidence that comprehensive nonpharmaceutical interventions implemented to control the transmission of severe acute respiratory syndrome coronavirus-2 also profoundly suppressed seasonal influenza epidemics. The sharp rebound of influenza activity after the relaxation of restrictions underscores the need for integrated preparedness strategies to manage concurrent threats from multiple respiratory viruses.