Overrepresentation of influenza A(H1N1)pdm09 virus among severe influenza cases in the 2011/12 season in four European countries Beauté, J and Broberg, E and Plata, F and Bonmarin, I and O’Donnell, J and Delgado, C and Boddington, N and Snacken, R, Eurosurveillance, 17, 20105 (2012), https://doi.org/10.2807/ese.17.09.20105-en