influenza virus antigenic data MC, 20101130: "Antibodies against the viral surface glycoprotein hemagglutinin (HA) provide protective immunity to influenza virus infection, and this protein is therefore the primary component of influenza vaccines. However, the antigenic structure of HA has changed significantly over time, a process known as antigenic drift (6), and in most years, the influenza vaccine has to be updated to ensure sufficient efficacy against newly emerging variants (7, 8). The World Health Organization coordinates a global influenza surveillance network, currently consisting of 112 national influenza centers and four collaborating centers for reference and research. This network routinely characterizes the antigenic properties of influenza viruses using a hemagglutination inhibition (HI) assay " Data reflecting the antigenic properties of influenza viruses characterized using a hemagglutination inhibition (HI) assay MC, 20101130: renamed antigenic data (from strain antigenic data) and moved under data item from strain specimen quality WEB: http://www.sciencemag.org/content/305/5682/371.full