Getting vaccinated against respiratory syncytial virus (RSV) around 32 weeks of pregnancy offers the best protection for newborn infants, according to a new study published in the American Journal of Obstetrics and Gynecology.
As of last year, RSV vaccination with Abrysvo has been recommended for pregnant women in the United States from 32 to 36 weeks gestation, at the end of the third trimester.
The passive antibodies provided to the newborn via the transplacental transfer of maternal antibodies offer significant protection against severe infection with the respiratory virus, which is the leading cause of hospitalization for US infants under 6 months of age.
'Much-needed data'
In the study, researcher from Mass General Brigham Hospital in Boston show that earlier in the 32-to-36-week timeframe is better.
"This work provides much-needed data to guide physicians in counseling patients about RSV vaccine timing during pregnancy," said study author Andrea Edlow, MD, a maternal-fetal medicine specialist at Massachusetts General Hospital in a Mass General Brigham press release.
"Our findings suggest that being vaccinated earlier within the approved timeframe allows for the most efficient placental transfer of antibody to the newborn. They also may have implications for when the RSV monoclonal antibody, Nirsevimab, should be administered to newborns."
5 weeks prior to delivery estimated to be best
Using blood samples from 124 women who received the RSV vaccine during weeks 32 to 36 of pregnancy and samples collected from 29 2-month-old infants of those mothers, the authors measured levels of RSV antibodies.
The authors found that maternal vaccination 2 to 3 weeks and 3 to 4 weeks prior to delivery was associated with significantly lower antibody transfer compared to levels seen in those with RSV vaccination at least 5 weeks before delivery.
Maternal RSV vaccination earlier in the approved 32-36 week window (to maximize the likelihood that at least 5 weeks elapse between vaccination and delivery) may confer the best possible protection for the neonate and infant.
"As RSV-specific antibody levels at birth have been demonstrated to be correlates of protection against RSV infection in infants too young to yet to receive their own vaccines, maternal RSV vaccination earlier in the approved 32-36 week window (to maximize the likelihood that at least 5 weeks elapse between vaccination and delivery) may confer the best possible protection for the neonate and infant," the authors concluded.
