Global Epidemiology of Human Adenoviruses, 2016-2024: A Pre- and Post-COVID-19 Analysis of Circulation Patterns and Epidemic Timing

Background: Human adenoviruses (HAdV) circulate globally, but their seasonal patterns remain poorly defined. We aimed to characterize the timing, amplitude, and duration of HAdV epidemics worldwide and to compare patterns before and after the COVID-19 pandemic. Methods: Virological surveillance data on HAdV were obtained from the WHO FluNet database: data from 65 countries were analyzed to estimate epidemic peak timing, amplitude, and duration across the Northern and Southern Hemispheres and the intertropical belt, comparing prepandemic (2016-2019) with postpandemic (2021-2024) periods. To ensure robustness, analyses were restricted to country-seasons with ≥ 30 reporting weeks. Results: From 2016 to 2024, 65 countries reported roughly 148,000 HAdV detections across 335 country-seasons; 46% of seasons had ≥ 50 detections. In the 20 countries with sufficient data for seasonality analyses, median epidemic duration was 31 weeks (range 5-42) and median peak amplitude 70% (40%-98%). Peak timing followed latitude: June-July in Southern Hemisphere, November-December in high-latitude Northern countries, March-April in lower latitude. After COVID-19, several countries showed marked timing shifts, with concurrent changes in amplitude. Conclusions: After the onset of the COVID-19 pandemic, the usual seasonal patterns of HAdV were altered, with pronounced shifts in peak timing across settings and latitudes. These results underscore the need for strong, ongoing, type-specific surveillance to guide public health strategies.