Clinical Pearls & Morning Reports
In the United States, the recommendations for maternal immunization include the inactivated influenza vaccine and the combined tetanus–diphtheria–acellular pertussis (Tdap) vaccine. In some other countries, pregnant women also receive hepatitis B vaccine, hepatitis E vaccine, or both. A new Review Article explains.
Q: What does the available evidence show regarding the immunogenicity of vaccines administered to pregnant women?
A: Evidence regarding the immunogenicity of vaccines administered to pregnant women, as compared with nonpregnant women, is mixed. In some studies, mainly involving inactivated influenza vaccine, equivalent responses were observed in pregnant and in nonpregnant women. Studies of vaccination against hepatitis B, influenza, pertussis, and yellow fever showed lower immunogenicity in pregnant women than in nonpregnant women.
Q: Is maternal immunization routinely incorporated into antenatal care in the United States?
A: Maternal vaccination in the United States is estimated to be approximately 50% for influenza nationally and 10% for Tdap in 16 states that have data on maternal Tdap vaccination.
A: There are emerging data on the effect of vaccine-induced maternal pertussis antibodies on infant DTaP responses. Small trials in the United States and Canada showed lower antibody responses to DTaP among infants whose mothers received Tdap during pregnancy than among the infants of unvaccinated women. In a small trial in Vietnam (where infants also received DTaP), antibodies against pertactin (an immunogenic virulence factor of Bordetella pertussis) but not against pertussis toxin and filamentous hemagglutinin, two other pertussis antigens, were lower in the infants of mothers who received Tdap during pregnancy. The clinical relevance of studies showing attenuation of vaccine responses in infants is uncertain, since there is no broadly accepted immunologic correlate of protection for pertussis. Nevertheless, these findings warrant monitoring of age-specific pertussis trends in populations with maternal pertussis immunization in order to detect any shifting disease burden from infants who are younger than 6 months of age to infants who are 6 months of age or older, as well as to children and adolescents.
A: In recent years, there has been an increase in efforts to develop vaccines for pregnant women. Vaccines against respiratory syncytial virus (RSV) and group B streptococcus have seen the most progress. There are several RSV vaccines in preclinical and clinical stages of development. Given that preterm infants are a high-risk group for adverse outcomes of RSV infection, recommendations concerning the gestational age for RSV vaccination will have to account for adequate antibody transfer for preterm infants. In recent decades, there have been multiple attempts at developing maternal group B streptococcal vaccines. The first-generation vaccines evaluated in clinical trials contained polysaccharide antigens and had heterogeneous immunogenicity. More recently, monovalent and trivalent conjugate vaccine candidates have been evaluated in clinical trials. The trivalent conjugate vaccine, which has undergone phase 1 and 2 trials, contains capsular serotypes Ia, Ib, and III. The vaccine was immunogenic and safe in these early-phase trials. Serotypes Ia, Ib, and III cover the majority of cases of group B streptococcal disease in infants in the Americas and Europe. However, the list of serotypes contributing to infant disease globally includes types II and V. Hence, a maternal group B streptococcal vaccine targeting the global, rather than regional, disease burden will require inclusion of these serotypes.