BACKGROUND: The maternal immunization platform has multiple vaccines already being utilized with more vaccines being considered. METHODS: We describe areas with knowledge gaps regarding maternal immunization including (1) pathogen, (2) vaccine product, (3) vaccine strategy, (4) implementation research and (5) Regulatory and Public Health Policy. RESULTS: Despite advances in clinical research during pregnancy, many questions remain regarding vaccine administration, products, coadministration of vaccines and vaccine acceptance. Issues regarding maternal antibody transfer in high-risk pregnancies need further study. CONCLUSIONS: Moving new maternal vaccines forward will take support from a broad array of experts.