Response to vaccination and immune status after intrauterine exposure to immunomodulating drugs for maternal IBD

Guidelines on inflammatory bowel disease (IBD) recommend continuing immunomodulating drugs during pregnancy, but their effects on the infant immune system remain uncertain. In this observational study, infants exposed to maternal IBD medication were vaccinated according to the Dutch National Immunization Program. We measured vaccine-specific IgG at 6 and 12 months and leukocytes, lymphocyte subsets, immunoglobulins, and infections at 2, 6, and 12 months of age. Vaccine responses and lymphocyte subsets were compared with historical cohorts and other outcomes with age-specific reference ranges. Vaccine responses following a 3 + 1 vaccination schedule were comparable to or higher than controls following a 2 + 1 schedule for all vaccine components, except filamentous haemagglutinin (FHA) and pneumococcal serotype 19 F. Neutropenia occurred more frequently than expected from reference values, but was self-limiting in all cases. The proportion of infants with T- or total B-cell lymphopenia did not differ from healthy controls. At 6 months, 9.8% of infants had mildly reduced total IgG concentrations, and low IgA was observed in 28.1%, 41.3%, and 15.4% at 2, 6, and 12 months, respectively; significantly more than expected based on reference values. The observed infection rate was similar to that reported in the literature. These findings may help develop clinical follow-up guidelines.