Determinants of epidemic size and the impacts of lulls in seasonal influenza virus circulation

• Published in: Nature communications Vol. 15; no. 1; p. 591
• Main Authors: de Jong, Simon P. J., Felix Garza, Zandra C., Gibson, Joseph C., van Leeuwen, Sarah, de Vries, Robert P., Boons, Geert-Jan, van Hoesel, Marliek, de Haan, Karen, van Groeningen, Laura E., Hulme, Katina D., van Willigen, Hugo D. G., Wynberg, Elke, de Bree, Godelieve J., Matser, Amy, Bakker, Margreet, van der Hoek, Lia, Prins, Maria, Kootstra, Neeltje A., Eggink, Dirk, Nichols, Brooke E., Han, Alvin X., de Jong, Menno D., Russell, Colin A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 18.01.2024; Nature Publishing Group; Nature Portfolio
• Subjects: 13/1; 631/114/2397; 692/699/255/1578; 692/700/478/174; Antibodies; Circulation; COVID-19; Disease transmission; Epidemics; Epidemiology; Humanities and Social Sciences; Humans; Influenza; Influenza A Virus, H1N1 Subtype; Influenza, Human - epidemiology; multidisciplinary; Pandemics; Prediction models; Public health; Science; Science (multidisciplinary); Seasons; Viral diseases; Viruses
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-44668-z

During the COVID-19 pandemic, levels of seasonal influenza virus circulation were unprecedentedly low, leading to concerns that a lack of exposure to influenza viruses, combined with waning antibody titres, could result in larger and/or more severe post-pandemic seasonal influenza epidemics. However, in most countries the first post-pandemic influenza season was not unusually large and/or severe. Here, based on an analysis of historical influenza virus epidemic patterns from 2002 to 2019, we show that historic lulls in influenza virus circulation had relatively minor impacts on subsequent epidemic size and that epidemic size was more substantially impacted by season-specific effects unrelated to the magnitude of circulation in prior seasons. From measurements of antibody levels from serum samples collected each year from 2017 to 2021, we show that the rate of waning of antibody titres against influenza virus during the pandemic was smaller than assumed in predictive models. Taken together, these results partially explain why the re-emergence of seasonal influenza virus epidemics was less dramatic than anticipated and suggest that influenza virus epidemic dynamics are not currently amenable to multi-season prediction. Seasonal influenza levels were unusually low when non-pharmaceutical interventions for COVID-19 were in place. Here, the authors analyse serological and epidemiological evidence for the hypothesis that such lulls in influenza transmission lead to reduced immunity and therefore larger epidemics in subsequent seasons.