Use of Antigenic Cartography in Vaccine Seed Strain Selection

Significance of Findings Human influenza A viruses are classic examples of antigenically variable pathogens that have a seemingly endless capacity to evade the host’s immune response. The viral hemagglutinin (HA) and neuraminidase (NA) proteins are the main targets of our antibody response to combat infections. HA and NA change continuously to escape from humoral immunity, a process known as antigenic drift. As a result of antigenic drift, the human influenza vaccine is updated frequently. The World Health Organization (WHO) coordinates a global influenza surveillance network that routinely characterizes the antigenic properties of circulating strains by the hemagglutination inhibition (HI) assay to select new seed viruses for such vaccine updates. To facilitate a quantitative interpretation and easy visualization of HI data, a new computational technique called ‘‘antigenic cartography’’ was developed. Since its development, antigenic cartography has been applied routinely to assist the WHO influenza surveillance activities. Until recently, antigenic variation was not considered a serious issue for influenza vaccines for poultry. However, because of the diversification of the Asian H5N1 lineage since 1996 into multiple genetic clades and subclades, and because of the long-term use of poultry vaccines against H5 in some parts of the world, this issue needs to be readdressed.