Ye C, et al. - Via conducting influenza-like illness (ILI) cases surveillance in two sentinel hospitals between 2012 and 2018 in Pudong New Area, Shanghai, researchers examined and compared the seasonality and epidemiological features of seasonal influenza subtypes after the 2009 A/H1N1 pandemic. In addition, they sought to lay a foundation for further investigation into the social and environmental factors affecting seasonal influenza transmission. Enrolling 10,977 ILI patients, they identified 2,385 (21.7%) laboratory-confirmed influenza cases. Influenza B (5.4%) was frequent among the ILI patients compared to influenza A (16.3%). During the six-year study period, they noted semiannual epidemic peaks in four years, while only one annual epidemic peak in the other two years. The subtropical region of China thus displays the complexity of seasonal influenza virus activity, presenting both semiannual and annual epidemic peaks in different years. These findings may assist in possible improvements in the timing of influenza vaccinations in Shanghai, China.