Impact of antenatal biological response modifying drugs on infant infection risk and vaccination rates: a national cohort study

Background The use of biological response modifying drugs (BRMDs) in women of reproductive age is increasing, with reassuring safety data during pregnancy. However, their long-term impact on infant immunity remains unclear, and recommendations regarding live-attenuated vaccines in exposed infants are inconsistent. We aimed to evaluate the association between antenatal BRMD exposure and infant infection risk during the first year of life, and to compare vaccination rates between exposed and unexposed infants. Methods This nationwide cohort study included all live births in Israel between January 2012 and October 2023. Infants exposed to BRMDs during the second or third trimester were compared with unexposed infants. Propensity score analysis was adjusted for maternal comorbidities and pregnancy and delivery characteristics. Cox regression modelling evaluated the dynamics post-delivery. Infection risk was evaluated using International Classification of Diseases-10 (ICD-10) codes and vaccination rates within the national childhood immunisation programme were assessed. Results Among 297 479 live births, 395 infants were exposed to BRMDs. No differences were observed in infection risk between exposed and unexposed infants (adjusted OR: 1.11; 95% CI 0.73 to 1.74; p=0.6), supported by Cox analysis (HR: 1.00; 95% CI 0.87 to 1.15; p>0.9). Rates of antibiotic use and hospitalisation were similar. However, the rotavirus vaccination rate was significantly lower in the exposed group (p<0.001), while vaccination rates for pneumococcal/hepatitis B/DTaP-IPV-Hib (diphtheria, tetanus, acellular pertussis-inactivated polio vaccine- haemophilus influenza B) vaccines were comparable between groups. Conclusion Antenatal exposure to BRMDs was not associated with increased infection risk in the first year of life but was linked to reduced uptake of the live-attenuated rotavirus vaccine.