Prospects for vaccines during pregnancy and in the newborn period

Abstract

Maternal and neonatal vaccine strategies have been used successfully throughout the world for many years. In addition, new vaccine technologies are likely to overcome the scientific issues related to safety, immunogenicity, and efficacy of neonatal vaccines. There are obvious advantages to maternal or neonatal immunizations. Immunologic protection in the first 8 to 12 weeks of life occurs only by passive immunization with IgG or by actively immunizing the mother or newborn baby (or by doing both as in hepatitis B). Although mothers may have protective levels of antibody to many pathogens, only active immunization of mothers or babies ensures that reliable protective levels are abundant in the neonate. Also, premature infants receive lower levels of passive maternal antibody and may not be protected regardless of maternal levels of specific antibodies. Thus, there is a particular need for development of neonatal immunization strategies in these babies. There is another value of neonatal immunization in the newborn period and that is compliance. In all areas of the world there is often poor compliance with infant vaccination policies. The newborn period offers the earliest possible time at which many infants can be reliably started on their immunization program. In many parts of the developing world this is already being put into practice for selected vaccines. Many of the vaccines currently used or under consideration for maternal or neonatal immunization are listed in Table 4. What are the impediments to progress in this area? For neonatal immunization there are several issues; however, the main impediment is providing vaccines that are safe, provide rapid protection, and are highly immunogenic if given to babies with an immature immune system. As reviewed in this article, current vaccines are safely and effectively used in newborn babies. As new vaccine technologies improve immunogenicity and allow mucosal delivery, the routine childhood immunization may move into the newborn period. Maternal immunization is a more complex issue. Currently available vaccines and new conjugate vaccines are immunogenic in women, and there is no convincing evidence of risk to the fetus by immunizing pregnant women with bacterial vaccines, toxoids, or inactive viral vaccines. The reduction in anti-PRP antibody in mothers receiving PRP-T conjugate vaccine within 4 weeks of a tetanus shot, however, demonstrates the necessity to demonstrate immunogenicity, safety, and efficacy of maternal immunization strategies before universal implementation. To hasten the availability and utilization of maternal vaccines, an increasing emphasis on research with increased funding should focus on vaccine development specifically to provide protection for infants in the first weeks of life (both maternal and neonatal vaccine strategies). The pharmaceutical industry, physicians, and the FDA must work together to develop guidelines for studies that will efficiently analyze the safety and efficacy of candidate vaccines. Liability issues also must be addressed so that physicians and the pharmaceutical industry can become comfortable with producing and employing vaccines that will protect babies at the earliest possible time.