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Interim 2019/20 influenza vaccine effectiveness: six European studies, September 2019 to January 2020.

Rose, A., Kissling, E., Emborg, H.D., Larrauri, A., McMenamin, J., Pozo, F., Trebbien, R., Mazagatos, C., Whitaker, H., Valenciano, M., Hooiveld, M. Interim 2019/20 influenza vaccine effectiveness: six European studies, September 2019 to January 2020. Eurosurveillance: 2020, 25(10)
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Background
Influenza A(H1N1)pdm09, A(H3N2) and B viruses were co-circulating in Europe between September 2019 and January 2020.

Aim
To provide interim 2019/20 influenza vaccine effectiveness (VE) estimates from six European studies, covering 10 countries and both primary care and hospital settings.

Methods
All studies used the test-negative design, although there were some differences in other study characteristics, e.g. patient selection, data sources, case definitions and included age groups. Overall and influenza (sub)type-specific VE was estimated for each study using logistic regression adjusted for potential confounders.

Results
There were 31,537 patients recruited across the six studies, of which 5,300 (17%) were cases with 5,310 infections. Most of these (4,466; 84%) were influenza A. The VE point estimates for all ages were 29% to 61% against any influenza in the primary care setting and 35% to 60% in hospitalised older adults (aged 65 years and over). The VE point estimates against A(H1N1)pdm09 (all ages, both settings) was 48% to 75%, and against A(H3N2) ranged from −58% to 57% (primary care) and −16% to 60% (hospital). Against influenza B, VE for all ages was 62% to 83% (primary care only).

Conclusions
Influenza vaccination is of continued benefit during the ongoing 2019/20 influenza season. Robust end-of-season VE estimates and genetic virus characterisation results may help understand the variability in influenza (sub)type-specific results across studies.