Rotavirus is the predominant cause of acute gastroenteritis in young children worldwide, estimated to cause 453,000 annual deaths. Two live oral rotavirus vaccines are available, Rotarix a human monovalent vaccine and Rotateq a pentavalent vaccine containing five human-bovine reassortant strains. Rotavirus vaccines were introduced into the Australian National Immunisation Program in July 2007. Each state and territory independently selected the rotavirus vaccine to include in its immunisation schedule.
Rotavirus strains are classified based on the two outer capsid proteins into G (glycoprotein, VP7) and P (protease sensitive, VP4) genotypes respectively; these proteins also elicit type-specific and cross-reactive neutralising antibody responses. A classification system based on the full genome; Gx-P[x]-Ix-Rx-Cx-Mx-Ax-Nx-Tx-Ex-Hx, is also used and enables insights into the evolution of circulating strains. Since 1997, the Australian Rotavirus Surveillance Program has conducted a laboratory based surveillance of circulating rotavirus strains. Prior to vaccine introduction, G1P[8] strains were the dominant type identified in 7 of 11 years, with G3P[8] and G9P[8] strains most common in the remaining years. Since vaccine introduction the dominant genotype has changed each year, with G1P[8], G2P[4] and G3P[8] representing the most dominant genotypes between 2008 and 2012. In 2013, G12P[8] strains emerged as the dominant genotype. In the post-vaccine era genotypes such as artiodactyl-like G10P[14] and novel reassortant G3P[8] strains have emerged as a cause of disease in Australian children. In addition, sporadic diarrhoea outbreaks caused by antigenically distinct G1P[8] strains and G2P[4] strains have occurred in the Northern Territory.
Changes in the genotype distribution and patterns of circulating strains have occurred since the introduction of the rotavirus vaccination in Australia. However, vaccine introduction has resulted in a dramatic decline in the number of confirmed cases of rotavirus and associated hospitalizations in Australian children.