Increased capabilities for genomic surveillance have provided fresh insights into the global evolution of viruses. Once international air travel resumed, seasonal flu demonstrated a remarkable resurgence, returning to pre-pandemic levels. Areas with fewer COVID-19 restrictions were linked to ongoing flu virus transmission.
Seasonal flu outbreaks significantly strain healthcare systems, resulting in over 5 million hospitalizations among adults annually. The current method for developing influenza vaccines involves thorough monitoring of circulating strains, which consistently migrate across continents. The COVID-19 pandemic created an unprecedented opportunity to analyze the effects on seasonal influenza during such outbreaks, thanks to the reduction in global human mobility.
A new study conducted by an international group of researchers, including members from the University of Oxford, Fudan University, and KU Leuven, integrated data on the spread and genetic characteristics of seasonal influenza alongside international travel trends. This approach allowed them to assess how long flu viruses lingered in various regions amid fluctuations in international travel and how their genetic diversity evolved before, during, and after the COVID-19 pandemic.
Globally, seasonal influenza levels fell during the COVID-19 pandemic due to restrictions on movement and social interactions. However, the swift rebound of the flu once air travel resumed showed that the virus remained largely active during the pandemic, benefitting from ongoing movements and the build-up of genetic diversity.
Zhiyuan Chen, the lead author from the University of Oxford and Fudan University, remarked: “It was astounding how quickly seasonal flu returned to pre-pandemic levels just a few years following the peak of the COVID-19 pandemic.”
Tropical regions such as South and East Asia facilitate year-round flu transmission, leading to a greater variety of flu strains and increased viral diversity overall. Enhanced genomic surveillance during the pandemic has shed light on the roles of other areas, like Africa and West Asia, in the global flu transmission network. These regions exhibited signs of prolonged transmission and experienced comparatively fewer restrictions, partly due to lower COVID-19 transmission rates.
Co-author Professor Moritz Kraemer from the Department of Biology and Pandemic Sciences Institute at the University of Oxford stated: “Thanks to the expanded genomic surveillance established during the COVID-19 pandemic, we now have deeper insights into the global distribution patterns of seasonal flu and other respiratory viruses. These innovative and large datasets are publicly accessible and create opportunities to understand the complex interactions of climate, co-circulating viruses, and human behavior.”
Furthermore, with enhanced global capabilities to monitor viruses, it may become easier to track seasonal influenza effectively. This can help minimize the risk of vaccine mismatches, support the development of more efficient interventions, and alleviate the burden of seasonal influenza on healthcare systems. This is particularly important as more regions become conducive to continuous influenza circulation due to changing climate conditions.
Co-author Professor Hongjie Yu from Fudan University emphasized: “Ongoing efforts should continue to focus on monitoring seasonal influenza viruses and other respiratory pathogens, especially in resource-limited areas. The surveillance systems established for seasonal respiratory pathogens may also play a crucial role in managing future pandemics.”
