Background: Influenza immunization during pregnancy provides protection to the mother and the infant. Studies in adults and children with inactivated influenza vaccine (IIV) have identified changes in immune gene expression that correlated with antibody responses.

Objective: To define baseline blood transcriptional profiles and changes induced by IIV in pregnant women and to identify correlates with antibody responses.

Methods: Pregnant women were immunized with IIV during the 2013-14 and 2014-15 seasons. Blood samples were collected on day (d) 0 (pre-vaccination), d1 and d7 post-vaccination for transcriptional profile analyses; and d0, d30, delivery and cord blood to measure antibody titers.

Results: Transcriptional analysis demonstrated overexpression of interferon-stimulated genes (ISGs) on d1 and of plasma cell genes on d7. Pre-vaccination ISGs expression and ISGs over-expressed on d1 significantly correlated with increased H3N2, B Yamagata and B Victoria antibody titers. Plasma-cell gene expression on d7 correlated with increased B Yamagata and B Victoria antibody titers. Compared with women vaccinated during the previous influenza season, women who were not vaccinated the prior year showed more frequent significant correlations between ISGs and antibody titers.

Conclusions: Influenza vaccination in pregnant women resulted in enhanced expression of ISGs and plasma cell genes that correlated with antibody responses.