Impact of non-pharmaceutical interventions of the COVID-19 pandemic on the trend of seasonal influenza in Kingdom of Saudi Arabia.

BACKGROUND: The implementation of non-pharmaceutical interventions (NPIs) during the COVID-19 pandemic has significantly affected the transmission dynamics of respiratory viruses globally. This study aimed to evaluate the impact of COVID-19 related NPIs on the trends of seasonal influenza in the Jazan region of southern Saudi Arabia. METHODS: A retrospective observational study was conducted from January 2017 to December 2023. Data on laboratory-confirmed cases of seasonal influenza and COVID-19 were obtained from the Saudi Ministry of Health databases. The analysis compared influenza activity before and during the COVID-19 pandemic, focusing on incidence fluctuations, demographic characteristics, and the timing relative to the implementation and relaxation of NPIs. RESULTS: Influenza cases declined from 449 in 2020 to 46 in 2021 (p < 0.001) during periods of strict NPI enforcement before rebounding to 430 in 2022 and 1,001 in 2023 (p < 0.001). COVID-19 cases peaked between 2020 and 2022 and showed a significant inverse correlation to influenza activity (p < 0.001). Influenza predominantly affected Saudis (88.7%) versus non-Saudis (11.3%) (p < 0.001), while COVID-19 cases were mainly among Saudis (84.3%) (p < 0.001). Age and gender distributions showed significant shifts post-NPI relaxation (p < 0.01), with influenza affecting 5-14-year-olds and 25-64-year-olds more prominently, and a gender shift from male to balanced or female predominance in recent years (p < 0.05). CONCLUSION: COVID-19 NPIs substantially reduced seasonal influenza transmission in the Jazan region. These findings highlight the collateral benefits of public health measures during pandemics and suggest that continued surveillance and targeted NPIs can be valuable in controlling seasonal influenza. Future strategies should integrate influenza vaccination campaigns with pandemic preparedness plans, considering regional specificities.