Several recent milestones have been reached in the regulatory aspects of the assessment of vaccines for use in pregnancy (27). It is clear that for both novel vaccines, as well as for currently licensed vaccines not previously evaluated in pregnant women, regulatory agencies approval for use during pregnancy would result in inclusion of specific information in the product label that would facilitate the acceptance and use of the vaccine by health-care providers and the public in general. One important step toward facilitating the utilization of vaccines in pregnancy is the recent update to the US FRA pregnancy and lactation labeling rule, whereby product label pregnancy risk categories designated with letters as A, B, C, D, and X that were difficult to put into practice have been replaced with a narrative descriptions of the risks of using the vaccine during pregnancy, as informed by any source of information, including both observational and prospective studies (28). In 2015, vaccine manufacturers sought guidance from the Vaccines and Related Biological Products Advisory Committee of the FDA to work toward the development of vaccines for maternal immunization. In their fall meeting, the determination was made that the regulatory approval process of vaccines indicated for maternal immunization to prevent infant disease would be guided by regulations outlined in Title 21 of the Code of Federal Regulations and standards set forth in applicable documents such as the ICH guidelines and FDA guidance documents (29). The groups agreed that the path to development and licensure of a vaccine for pregnant women would be product specific and designed to support the indication being sought. Key aspects to consider would include the use of serologic endpoints as markers of passive protection in the infants, the evaluation of duration of immunity and immune interference with childhood vaccines, and the duration and type of safety follow-up. Importantly, the committee considered that observational studies could be used as an approach to confirm the effectiveness of already licensed vaccines that are recommended for use in pregnancy in the US.