The hemagglutinin esterase glycoprotein is the principal protective antigen of the infectious salmon anemia virus and is widely used in the development of prophylactic vaccines for Atlantic salmon and other salmonids. Expression of the hemagglutinin esterase gene in recombinant systems, including deoxyribonucleic acid vaccines, viral-vectored vaccines and plant-based expression platforms, is intended to induce protective immune responses against infection. As the primary antigenic determinant of the virus, the protein is also used in diagnostic assays and molecular epidemiology studies. Variations within the highly polymorphic region of the hemagglutinin esterase gene are used to classify virus strains and have been associated with differences in pathogenicity.