This memo and subsequent guidance spelled out the critical need to conduct preclinical studies in animal models to assess reproductive and developmental toxicity “prior to licensure of vaccines intended for maternal immunization and/or women of childbearing age”. However, the documents admitted that “lack of adverse effects on embryo/fetal development in an animal study does not necessarily imply absence of risk for humans.” Moreover, given the FDA’s emphasis that all of the recommendations included in its guidance are non-binding, the extent to which vaccine manufacturers choose to abide by them is largely unknown.