A new study from Mass General Brigham suggests that administering the respiratory syncytial virus (RSV) vaccine earlier in pregnancy, specifically around 32 weeks, may provide the best protection for newborns against this potentially severe virus. The findings, published in the American Journal of Obstetrics & Gynecology, challenge current guidelines that recommend vaccination between 32 and 36 weeks of gestation.
RSV, which typically causes mild, cold-like symptoms in adults, can lead to serious illness in infants and is a leading cause of hospitalization among U.S. infants. While it is known that maternal vaccination is crucial for protecting newborns, the optimal timing for administering the RSV vaccine during pregnancy has been uncertain. Previous clinical trials studied a broader gestational age range, but the approved vaccination window was narrower, highlighting the need for more specific guidance on timing.
Dr. Andrea Edlow, a maternal-fetal medicine specialist at Massachusetts General Hospital and senior author of the study, noted that prior research on COVID-19 mRNA vaccines indicated that the timing of maternal vaccination significantly affects both maternal immune responses and the transfer of antibodies to the fetus. To explore whether this principle applies to RSV vaccination, Edlow and her team measured RSV antibody levels in umbilical cord blood at delivery among 124 women vaccinated during the 32-36 week window, as well as in the blood of 29 two-month-old infants born to these mothers. All participants received care at Massachusetts General Hospital or Mount Sinai Health System in New York City.
The study revealed that women who received the RSV vaccine at least five weeks before delivery had the most effective transfer of antibodies to their newborns, compared to those vaccinated two to three or three to four weeks prior to delivery.
In a further analysis, the researchers compared RSV antibody levels in mothers and their newborns who were vaccinated to those in 20 unvaccinated mothers. The results showed that maternal vaccination significantly increased both maternal and cord blood RSV antibody levels, with these levels remaining elevated for a longer duration.
“This work provides much-needed data to guide physicians in counseling patients about RSV vaccine timing during pregnancy,” said Dr. Edlow. “Our findings suggest that earlier vaccination within the approved timeframe optimizes placental antibody transfer to the newborn. This may also have implications for the timing of RSV monoclonal antibody, Nirsevimab, administration to newborns. Further research is warranted for other vaccines given during pregnancy.”
Conclusion
The researchers emphasized the need for additional studies to determine the minimum antibody levels required for adequate protection against RSV in infants. They also highlighted the potential added protection from breast milk produced by RSV-vaccinated mothers. While this study focused on antibody transfer, larger studies involving infants aged two to six months are necessary to assess the extent to which maternal vaccination enhances protection against RSV.
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