Researchers Highlight the Best Time for RSV Vaccine During Pregnancy - Video

Current guidelines recommend that pregnant people receive a vaccine against respiratory syncytial virus (RSV)-which typically causes mild, cold-like symptoms in most adults but can be deadly for infants during weeks 32–36 of pregnancy. New research led by investigators at Mass General Brigham suggests that vaccination earlier in that timeframe, closer to 32 weeks, could provide the best protection for newborns against

RSV. The findings are published in the American Journal of Obstetrics & Gynecology.

To assess whether maternal vaccine timing is an important consideration for RSV vaccination, the investigators measured RSV antibodies in the umbilical cord at the time of delivery among 124 women who received the RSV vaccine during weeks 32–36 of pregnancy and in the blood of 29 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 City. Levels of RSV antibodies can predict protection against RSV infection in infants too young to yet receive their own vaccines.

The investigators found that maternal RSV vaccination at least 5 weeks prior to delivery led to the most efficient transfer of maternal antibodies across the placenta to the newborn, compared with maternal vaccination at 2-3 or 3-4 weeks prior to 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 study was designed to measure antibody transfer, but larger studies of infants 2 to 6 months of age will be needed to determine the extent to which this leads to enhanced protection.

Reference: JASSET, O. J., ZAPANA, P. A. L., BAHADIR, Z., SHOOK, L., DENNIS, M., GILBERT, E., ... & EDLOW, A. G. (2024). Enhanced placental antibody transfer efficiency with longer interval between maternal RSV vaccination and birth. American Journal of Obstetrics and Gynecology.