Positions of amino acids in NA that have changed since 2009. Positions of amino acids in NA that have changed since 2009. The image is of an NA dimer (side view). Amino acids that were identified as critical for MAb binding are shown in purple (248 and 369) or red (249, 273, and 451). Additional amino acids on the surface of NA that differ between CA/09 and MI/15, the virus most recently recommended for production of the A/H1N1pdm component of seasonal influenza vaccines, are identified on the same dimer in aqua or dark gray. Jin Gao et al. mBio 2019; doi:10.1128/mBio.00307-19