How Has the COVID-19 Pandemic Affected the Influenza Seasonality Patterns in Different Climate Regions?-A Time-Series...

Due to the burden of influenza, significant efforts have been made to understand its geographical and temporal patterns to advise influenza prevention. Influenza temporal patterns have been affected since the emergence of COVID-19, presumably attributed to nonpharmacological interventions (NPIs). Understanding the changes in influenza activity before and during the COVID-19 pandemic in different climate regions is urgently needed to inform decision-making in future influenza control measures and prevention policies.

This study analysed influenza surveillance data (2012-2022) collected from the FluNet database to compare the patterns of long-term influenza activity in nine selected temperate and tropical countries. The long-term influenza activity in each country was compared before and after the emergence of COVID-19. The level of NPI stringency was measured using the stringency index (SI). Interrupted time series (ITS) analyses were performed to quantify the impact of COVID-19 NPIs on the changes in influenza patterns before and after the stringent implementation of NPIs in the selected countries.

Before the COVID-19 pandemic, influenza activity in temperate countries appeared in winter, while the seasonality patterns in tropical countries were irregular and lasted longer than in temperate countries. During the pandemic, influenza cases decreased drastically in all selected countries, even though the amount of influenza testing remained adequate. The ITS results confirmed a significantly inverse relationship between stringency of NPIs and influenza activity. Although influenza cases have reemerged following the removal of NPIs, the patterns of influenza activity worldwide remain undergoing transitioning shifts post-pandemic. International collaboration is needed to continue monitoring future changes in influenza patterns to prevent large outbreaks.

There has been a change in the temporal patterns of influenza activity worldwide after the pandemic. NPIs have shown a significant effect in reducing influenza activity in all selected countries.