6 October 2025

Key points

  • Seasonal influenza is, as the name says, seasonal — it generally means the winter flu, and in Hong Kong the peak runs from January to March.
  • A summer flu does not come every year: over the past ten years only about half had one, usually in July or August.
  • 2025 was late. The Department of Health announced only on 9 September that Hong Kong had formally entered its summer influenza peak.
  • Past data puts a summer peak at anywhere from a month and a half to four months. Counting from 9 September, a four-month run could overlap the winter peak around January.
  • If the summer and winter peaks do overlap, severe cases and hospital admissions are likely to run higher than in previous years.