Although our finding that recombinant N8-JD13-WT forms a mixture of open and closed tetramers (Fig. 1c) is consistent with a previous report showing that N8 NAs can form monomers and dimers, a number of infection-elicited N8 NA-specific antibodies recognized a quaternary epitope23, providing an incentive for tetramer stabilization. Here, XK is linked to infection.