Seasonal influenza epidemics impose substantial burdens on healthcare systems and cause >5 million hospitalizations of adults each year. The current approach to influenza vaccine development requires comprehensive surveillance of circulating strains, which are constantly moving from continent to continent. The reduction in global human mobility during the COVID-19 pandemic provided a unique opportunity to evaluate how seasonal influenza is impacted during pandemics.
In this new study, an international team of researchers, including from the University of Oxford, Fudan University, and KU Leuven, combined data on the spread of seasonal influenza, its genetic makeup, and international travel patterns to study how seasonal flu viruses moved and evolved. This approach helped to estimate how long the viruses remained in certain regions during periods of high and low volumes of international travel and how their genetic diversity changed before, during, and after the COVID-19 pandemic. During the COVID-19 pandemic, seasonal influenza levels dropped worldwide due to COVID-19 pandemic-related restrictions on population movement and mixing.
However, the subsequent rapid bounce back of influenza once air travel returned to pre-pandemic levels showed that the virus was in most cases maintained during the pandemic with continued viral movements and accumulation of genetic diversity. It was remarkable how quickly seasonal flu re-established to a pre-pandemic equilibrium just a few years af.
