Inflammatory bowel disease (IBD) treatments and pregnancy can independently modulate immune responses, but the combined effects on SARS-CoV-2 vaccine-induced immunity are poorly understood. This study explores the efficacy of SARS-CoV-2 vaccination and placental antibody transfer among pregnant women with IBD on biologic therapies. This observational study included pregnant women with and without IBD from the PIANO and PREVENT-COVID studies and their neonates. We assessed anti-SARS-CoV-2 neutralizing antibody titers (NT50) in maternal and cord blood post-vaccination using a pseudotype neutralization assay and calculated placental transfer ratios. A total of 32 pregnant women participated, and 27 were exposed to a biologic medication during pregnancy. Neutralizing antibody titers were similar between biologic-treated and non-treated groups, and biologic-exposed women demonstrated robust placental transfer of neutralizing antibodies. Corticosteroid use during pregnancy was significantly associated with reduced placental transfer efficiency, although this effect was not significant in a sensitivity analysis excluding patients treated with immunomodulators. Vaccination timing and previous SARS-CoV-2 infection impacted maternal and cord antibody levels, with higher titers observed in those vaccinated before pregnancy or infected during pregnancy. Overall, our findings suggest that pregnant women with IBD on biologic therapies mount effective SARS-CoV-2 neutralizing antibody responses similar to their non-biologic-exposed counterparts, with efficient placental transfer. These findings support the safety and efficacy of SARS-CoV-2 vaccination in this population, although further research with larger cohorts is needed to explore the long-term protective effects of transferred antibodies in neonates. Corticosteroid use, immunomodulator use, and vaccination timing may influence antibody dynamics, underscoring the need for tailored clinical management in this vulnerable population.

D.E.L. has received consulting fees from Neptune Medical. M.K. receives research support from Eli Lilly for work unrelated to this submission. M.K. is a member of the scientific advisory boards of Santa Ana Bio and Switchback Therapeutics and has received consulting fees from Cellarity, Spyre Therapeutics, Morphic Therapeutic, Sonoma Biotherapeutics, and Surrozen. M.D.L. receives research support from Lilly, Takeda, and Pfizer and is a consultant for AbbVie, BMS, Celltrion, Janssen, Intercept, Lilly, Pfizer, Prometheus, Takeda, and Target RWE. U.M. is a consultant for Abbvie, Bristol Myers Squibb, Boeringher Ingelheim, Celltrion, Enveda, Gilead, Janssen, Lilly, Pfizer, Protagonist, Roivant, and Takeda, and advises for Rani Therapeutics (SAB) and Merck/Prometheus Biosciences (DSMB). J.J.: none to report. C.S.C.: none to report.

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The study was conducted according to Declaration of Helsinki principles and was approved by the Institutional Review Board of the University of California, San Francisco (#10-00831). Written informed consent was received from participants prior to inclusion in the study.

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