Current guidelines recommend that pregnant people receive a respiratory syncytial virus (RSV) vaccine –; which usually causes mild, cold-like symptoms in most adults, but can be fatal for infants –; New research by investigators at Mass General Brigham suggests that vaccination earlier in this time frame, closer to 32 weeks, may provide the best protection for newborns against RSV. The results are published in the American Journal of Obstetrics and Gynecology.
Receiving the RSV vaccine during pregnancy is an important way for mothers to protect their newborns and infants from RSV, the leading cause of hospitalization among infants in the United States. However, it was unclear whether this equated to vaccinating at any time during the approved window, or whether specific weeks were most optimal. Because the RSV vaccine was ultimately approved for administration during a narrower gestational age window than initially studied in the large clinical trial, more information was needed on how maternal antibodies travel across the placenta. ‘week to week through the approved window.
Andrea Edlow, MD MSc, lead author, maternal-fetal medicine specialist in the Department of Obstetrics and Gynecology at Massachusetts General Hospital, founding member of the Mass General Brigham Health System
Edlow and his team’s previous work evaluating prenatal administration of COVID-19 mRNA vaccines demonstrated that the timing of maternal vaccination was associated with altered maternal responses and transplacental transfer of antibodies to the fetus. To assess whether maternal vaccination schedule is also an important consideration for RSV vaccination, investigators measured RSV antibodies in the umbilical cord at the time of delivery in 124 women who received the RSV vaccine at during weeks 32 to 36 of pregnancy and in the blood of 29 women. 2-month-old infants of these mothers. All study participants were receiving care at Massachusetts General Hospital or Mount Sinai Health System in New York. Anti-RSV antibody levels may predict protection against RSV infection in infants too young to receive their own vaccines.
Investigators found that maternal RSV vaccination at least 5 weeks before delivery resulted in the most effective transfer of maternal antibodies across the placenta to the newborn, compared with maternal vaccination 2 to 3 or 3 to 4 weeks before delivery.
In an additional analysis, RSV antibody levels in maternal and cord blood after RSV vaccination were compared with RSV antibody levels in 20 unvaccinated mothers. Maternal RSV vaccination resulted in significantly higher and longer-lasting maternal and cord RSV antibody levels.
“This work provides much-needed data to guide physicians in counseling patients on the timing of RSV vaccination during pregnancy,” Edlow said. “Our results suggest that being vaccinated earlier than the approved time frame allows for the most effective placental transfer of antibodies to the newborn. They may also have implications for when the RSV monoclonal antibody Nirsevimab should be given to newborns. Similar research should be conducted. for other vaccines administered during pregnancy.
The investigators noted that additional studies are needed to determine the minimum amount of antibody transfer and/or blood antibody levels in infants necessary to adequately protect infants against RSV. It will also be important to understand the potential additive protection provided to infants by breast milk from mothers vaccinated against RSV. This study was designed to measure antibody transfer, but larger studies of infants aged 2 to 6 months will be needed to determine the extent to which this leads to enhanced protection.
