End-of-season influenza vaccine effectiveness in adults and children, United Kingdom, 2016/17

Pebody, Richard and Warburton, Fiona and Ellis, Joanna and Andrews, Nick and Potts, Alison and Cottrell, Simon and Reynolds, Arlene and Gunson, Rory and Thompson, Catherine and Galiano, Monica and Robertson, Chris and Gallagher, Naomh and Sinnathamby, Mary and Yonova, Ivelina and Correa, Ana and Moore, Catherine and Sartaj, Muhammad and de Lusignan, Simon and McMenamin, Jim and Zambon, Maria (2017) End-of-season influenza vaccine effectiveness in adults and children, United Kingdom, 2016/17. Eurosurveillance, 22 (44). ISSN 1560-7917 (https://doi.org/10.2807/1560-7917.ES.2017.22.44.17...)

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Introduction The United Kingdom is in the fourth season of introducing a universal childhood influenza vaccine programme. The 2016/17 season saw early influenza A(H3N2) virus circulation with care home outbreaks and increased excess mortality particularly in those 65 years or older. Virus characterisation data indicated emergence of genetic clusters within the A(H3N2) 3C.2a group which the 2016/17 vaccine strain belonged to. Methods: The test-negative case-control (TNCC) design was used to estimate vaccine effectiveness (VE) against laboratory confirmed influenza in primary care. Results: Adjusted end-of-season vaccine effectiveness (aVE) estimates were 39.8% (95% confidence interval (CI): 23.1 to 52.8) against all influenza and 40.6% (95% CI: 19.0 to 56.3) in 18-64-year-olds, but no significant aVE in ≥ 65-year-olds. aVE was 65.8% (95% CI: 30.3 to 83.2) for 2-17-year-olds receiving quadrivalent live attenuated influenza vaccine. Discussion: The findings continue to provide support for the ongoing roll-out of the paediatric vaccine programme, with a need for ongoing evaluation. The importance of effective interventions to protect the ≥ 65-year-olds remains.