Interim estimate of influenza vaccine effectiveness in hospitalised children, Hong Kong, 2017/18.

We conducted a hospital-based test-negative study in Hong Kong to estimate influenza vaccine effectiveness (VE) for the winter of 2017/18. The interim analysis included data on 1,078 children admitted between 4 December 2017 and 31 January 2018 with febrile acute respiratory illness and tested for influenza. We estimated influenza VE at 66% (95% confidence interval (CI): 43-79) overall, and 65% (95% CI: 40-80) against influenza B, the dominant virus type (predominantly B/Yamagata).