Rotavirus incidence and genotype distribution before and after national rotavirus vaccine introduction in Belgium.

Rotarix™ was introduced into the Belgian market in 2006 and RotaTeq™ in 2007, quickly reaching more than 85% vaccine coverage of all newborns in Belgium. The incidence of rotavirus gastroenteritis has been monitored in the Gasthuisberg University Hospital (GUH), Belgium since 1986, and since 1999 the genotypes of circulating rotavirus strains have been determined. The average percentage of rotavirus positive cases out of all hospitalized gastro-enteritis cases tested (>95% of these cases are younger than 5 years old) at the GUH between 1986 and 2006 was 19.0%. This percentage dropped to 12.4%, 9.6% and 6.4% in the three seasons post vaccine introduction (2006-2009), which is a decline of 34.7%, 49.4% and 66.3% respectively. In addition the rotavirus season was found to be shortened and delayed. The prevalence of the G2 genotype sharply increased in the 2006-2007 rotavirus season compared to the previous seasons and remained high (30-40%) in the 2007-2008 and 2008-2009 seasons. Rotavirus vaccines have strongly reduced the number of children hospitalized due to a rotavirus infection at the GUH; it is however unclear if the predominance of G2 genotypes is related to the vaccine introduction, or if this is attributable to normal genotype fluctuations. Continued surveillance will be pivotal to answer this question in the future.