Josephine van Dongen

Chapter 4 92 Abstract Objective Rotavirus vaccination has 87-100% effectiveness against severe rotavirus acute gastroenteritis (AGE), in healthy infants in high-income countries. Little is known whether infants with medical risk conditions (MRC) are equally protected.We conducted a quasi-experimental prospective multicenter before-after cohor t-study to assess the vaccine effectiveness (VE) of the human rotavirus vaccine (HRV) among MRC infants. Methods HRV was implemented in routine care for MRC infants in 13 Dutch hospitals. Par ticipants in the before and after cohor t, HRV unvaccinated and vaccinated respectively, were followed for occurrence of (rotavirus) AGE.VE of at least one dose was estimated using time-to-event analysis for severe rotavirus AGE. Vaccine impact on rotavirus hospitalizations comparing pre- and post-implementation periods was also assessed. Results 631 and 851 high-risk infants with MRC par ticipated in the before and after cohor ts, respectively. In total, 1302 infants were premature (88.3%), 447 small for gestational age (30.2%) and 251 had at least one congenital disorder (17.0%).VE against severe rotavirus AGE was 30% (95%CI -36;65%) and -2% (95%CI -50;31%) against rotavirus AGE of any severity. Overall, the observed number of rotavirus hospitalizations was low and not significantly different between the cohor ts (2 and 2, respectively). Conclusion In contrast to previous findings among healthy term infants, the routine use of human rotavirus vaccine in vulnerable medical risk infants offers limited protection against severe rotavirus gastroenteritis. Our study highlights the impor tance of studying vaccine performance in subgroups of medical risk infants separately.