Global patterns and drivers of influenza decline during the COVID-19 pandemic - Institut Pierre Louis d'Epidémiologie et de Santé Publique
Article Dans Une Revue International Journal of Infectious Diseases Année : 2023

Global patterns and drivers of influenza decline during the COVID-19 pandemic

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Abstract Influenza circulation declined during the COVID-19 pandemic. The timing and extent of decline and its association with interventions against COVID-19 were described for some regions. Here, we provide a global analysis of the influenza decline between March 2020 and September 2021 and investigate its potential drivers. We computed influenza change by country and trimester relative to the 2014-2019 period using the number of samples in the FluNet database. We used random forests to determine important predictors in a list of 20 covariates including demography, weather, pandemic preparedness, COVID-19 incidence, and COVID-19 pandemic response. With a regression tree we then classified observations according to these predictors. We found that influenza circulation decreased globally, with COVID-19 incidence and pandemic preparedness being the two most important predictors of this decrease. The regression tree showed interpretable groups of observations by country and trimester: Europe and North America clustered together in spring 2020, with limited influenza decline despite strong COVID-19 restrictions; in the period afterwards countries of temperate regions, with high pandemic preparedness, high COVID-19 incidence and stringent social restrictions grouped together having strong influenza decline. Conversely, countries in the tropics, with altogether low pandemic preparedness, low reported COVID-19 incidence and low strength of COVID-19 response showed low influenza decline overall. A final group singled out four “zero-Covid” countries, with the lowest residual influenza levels. The spatiotemporal decline of influenza during the COVID-19 pandemic was global, yet heterogeneous. The sociodemographic context and stage of the COVID-19 pandemic showed non-linear associations with this decline. Zero-Covid countries maintained the lowest levels of reduction with strict border controls and despite close-to-normal social activity. These results suggest that the resurgence of influenza could take equally diverse paths. It also emphasises the importance of influenza reseeding in driving countries’ seasonal influenza epidemics.
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hal-03918029 , version 1 (23-09-2024)

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Francesco Bonacina, Pierre-Yves Boëlle, Vittoria Colizza, Olivier Lopez, Maud Thomas, et al.. Global patterns and drivers of influenza decline during the COVID-19 pandemic. International Journal of Infectious Diseases, 2023, 128, pp.132-139. ⟨10.1016/j.ijid.2022.12.042⟩. ⟨hal-03918029⟩
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