Josephine van Dongen

4 Rotavirus vaccine effectiveness 93 Introduction Rotavirus is a frequent cause of acute gastroenteritis (AGE) in children below five years of age. 1 Since the global introduction of vaccines against rotavirus in 2006, hospitalizations for rotavirus AGE have decreased substantially. 2 Worldwide, over 98 countries have now included rotavirus vaccination in their national immunization program. 3 The majority of countries use one of two globally licensed live-attenuated oral rotavirus vaccines; Rotarix© or RotaTeq©. In high income countries, high rotavirus vaccine effectiveness (VE) against severe rotavirus AGE has been consistently repor ted for both vaccines with overall VE of more than 80% for a full series of either vaccine. 4–6 Yet, these estimates are primarily based on results from healthy infants. 4–6 There is however limited data on the performance of rotavirus vaccines in infants with underlying medical conditions that may influence their vaccine response and/or their risk of severe rotavirus AGE.These include premature infants, infants born small for gestational age and those with severe congenital disorders.There is reason to assume, vaccine responsiveness may be attenuated in these infants because of immaturity or conditions compromising immune responses to some extent due to their MRC. 7–9 Infants diagnosed with one or more of these medical risk conditions (MRC) represent eight percent of the Dutch bir th cohor t. 10 An earlier study showed these infants are at increased risk of severe or complicated rotavirus AGE. 10 In the absence of universal rotavirus vaccination in the Netherlands we star ted a pilot with rotavirus vaccination implemented in routine neonatal/ infant care for MRC infants.The human rotavirus vaccine (HRV, Rotarix©) was used throughout the project. This implementation was combined with a before-after cohor t study to evaluate rotavirus VE of at least one dose in high-risk infants with one or more MRC, with a focus on premature infants. Patients and methods The RIVAR (Risk group InfantVaccination Against Rotavirus) project piloted the implementation of a selective rotavirus vaccination program for MRC infants in pediatric secondary and ter tiary care hospitals.The primary objectives of the RIVAR project were 1) to assess the feasibility of implementing and executing this selective rotavirus vaccination program in routine hospital and outpatient care for MRC infants and, 2) to determine vaccine effectiveness (VE) against severe rotavirus AGE in MRC infants. Here, we describe the results of the step-wedge before-after cohor t study that was designed to assess the primary endpoint of VE. The study protocol was registered in the Dutch trial registry. 11