Abstract
BACKGROUND: In Italy, influenza viruses typically circulate from October to April, causing seasonal epidemics. The pattern of influenza virus circulation varies each season regarding the timing of the first case notification, period of circulation, and predominant influenza virus types and subtypes. METHODS: This analysis used comprehensive data from the national influenza surveillance network for the 2017/2018 to 2023/2024 influenza seasons in the Veneto Region. Influenza A (IAV) and B (IBV) viruses were detected and subtyped using real-time reverse transcriptase-polymerase chain reaction assays. RESULTS: Of 21,180 oropharyngeal swabs collected from 2017 to 2024, 4,325 (20.42%) were positive for influenza viruses. IAV accounted for 78.68% of positive cases overall, representing more than 65% of cases in every season except 2017/2018 (26.72%). Both A(H1N1)pdm09 and A(H3N2) subtypes were detected in all seasons with varying proportions. IBV represented 21.32% of all positive cases, with Victoria and Yamagata lineages detected simultaneously during the 2017/2018 season. No Yamagata lineage was detected after the 2018/2019 season, and no IBV cases were detected in the 2021/2022 season. In almost all seasons, influenza virus circulation was more significant in adults, especially those 65 years and older, than in children. CONCLUSIONS: In the Veneto Region, influenza virus circulation varied considerably from 2017/2018 to 2023/2024. In the 2020/2021 season, no influenza-positive samples were detected due to circulation of SARS-CoV-2 and related countermeasures. IAVs were the predominant type in most seasons, while IBVs made a limited contribution to the overall disease burden.