The enzyme kinetics of the neuraminidase was measured in duplicate for each strain as described in [61] , using the MUNANA reagent (4-methyl-umbelliferyl-N-acetyl neuraminic acid (Sigma-Aldrich, St-Louis, CO, #M8639)). Briefly, 10mL of live viruses diluted to 1:2|10 6 PFU mL were incubated at 37 0 C in Opaque Black Microfluor B CS50 96-well plates (VWR, Montreal, QC, #62402-983) with 30mL of MUNANA reagent ranging from 0 to 3000mM final concentration and 10mL of enzyme buffer [1:1 mix of 325mM MES (2-[N-Morpholino]ethanesulfonic acid) pH 6.5 (Sigma-Aldrich, St-Louis, CO, #M8250) and 10mM CaCl 2 (Sigma-Aldrich, St-Louis, CO)]. Fluorescence was measured in a Viktor 3 Multilabel Counter (PerkinElmer, Waltham, MA) every 90 seconds for 45 minutes. The excitation wavelength was 365nm and the emission wavelength 450nm with a 2:5nm excitation slit and a 20nm emission slit. K m and V max were calculated using a homemade Excel macro, created following [62] , and confirmed using the built-in ''Enzyme Kinetics'' features of the GraphPad Prism 5.01 software (GraphPad Software, La Jolla, CA).