Effect of monovalent rotavirus vaccine on rotavirus disease burden and circulating rotavirus strains among children in Morocco.

Rotarix(TM) vaccine was introduced into the National Program of Immunization of Morocco in October 2010, reaching quickly 87% of the target population of children nationally. The incidence of rotavirus gastroenteritis and the prevalence of circulating rotavirus strains has been monitored in three sentinel hospitals since June 2006. The average percentage of rotavirus positive cases among all children under 5 years old hospitalized for gastroenteritis during the pre-vaccine period (2006-2010) was 44%. This percentage dropped to 29%, 15% and 24% in the 3 years post vaccine introduction (2011, 2012 and 2013), which is a decline of 34%, 66%, and 45%, respectively. Declines in prevalence were greatest among children 0-1 years of age (53%) and were most prominent during the winter and autumn rotavirus season. The prevalence of the G2P[4] and G9P[8] genotype sharply increased in the post vaccine period (2011-2013) compared to the previous seasons (2006-2010). Rotavirus vaccines have reduced greatly the number of children hospitalized due to rotavirus infection at the three sentinel hospitals; it is however unclear if the predominance of G2P[4] and G9P[8] 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.