Josephine van Dongen

Chapter 6 144 Netherlands who did or did not receive rotavirus vaccination in a quasi-experimental setting. Methods For a detailed description of the study we refer to a previous publication ( chapter 4 ). In shor t, thir teen Dutch hospitals with a neonatal intensive or high care ward par ticipated in the project that combined the implementation of rotavirus vaccination program for medical risk infants with a prospective before-after cohor t study. During both periods with and without rotavirus vaccination, infants were recruited at six weeks of age if they had at least one medical risk condition; 1) prematurity (gestational age < 36 weeks), 2) low bir thweight (< 2500 grams) and/ or 3) congenital pathology (list in chapter 4 ), and received prolonged pediatric care between six and 14 weeks of postnatal age at the par ticipating site. Hospitals entered the study in a stepped-wedge approach and each site implemented rotavirus vaccination in routine care for medical risk infants between months 12-18 of the project. The schedule for other routine childhood immunizations according to the National Immunization Program (NIP) was left unchanged ( Figure 1 ). Post-implementation, the human rotavirus vaccine (HRV, Rotarix, GSK, Belgium) was used at all sites. HRV was given in a two-dose schedule, with first dose preferably between six and nine weeks of age and the second dose with a minimum interval of four weeks and no later than 24 weeks of age. The first dose was administered by a physician in par ticipating hospitals, the second dose was given by parents at home after detailed instruction. Figure 1. Vaccination schedule RIVM@2021. Legend: Rotarix = human rotavirus vaccination Abbreviations: DTaP-IPV = Diphteria Tetanus accelular Per tussis-Inactivated Polio vaccine, Hib = Haemophilus influenza type B, HBV = Hepatitis B vaccine, and PCV = Pneumococcal conjugate vaccine.