The Centre for Health Protection (CHP) of the Department of Health said on August 9 that it was investigating a severe paediatric influenza A infection in a five-year-old girl with underlying illnesses. She developed fever, cough with sputum, chills, rigors and shortness of breath on August 7 and was taken to Tuen Mun Hospital's accident and emergency department the next day, then admitted to the paediatric intensive care unit. Her respiratory specimen tested positive for influenza A (H1), and her clinical diagnosis was influenza A infection complicated by sepsis. She remained hospitalised in serious condition, the CHP said.

According to the CHP's preliminary investigation, the girl had received the 2025/26 seasonal influenza vaccination and had no travel history during the incubation period. Her household contacts remained asymptomatic, and the CHP said it would continue investigating.

CHP Controller Dr Edwin Tsui said Hong Kong entered the influenza season in late June and that activity was then high, with 9.94 per cent of respiratory specimens testing positive for seasonal influenza viruses and an influenza admission rate in public hospitals of 0.73 cases per 10 000 population the previous week. Influenza A (H3) and A (H1) each accounted for 45 per cent of detections, with influenza B at 10 per cent. He said activity was expected to remain high in the coming weeks and noted that 2026/27 vaccine procurement had been completed.