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- Posted October 20, 2025
RSV Antibody Shot Safe For Infants Even If Mom Was Vaccinated During Pregnancy, Experts Say
Babies can be safely administered antibody protection against respiratory syncytial virus (RSV) after birth even if their moms had RSV vaccination while pregnant, a new study says.
An antibody shot called nirsevimab (Beyfortus) is available after delivery to provide babies with protection against RSV, a respiratory infection that is the most common cause of hospitalization among infants.
However, prior research had not investigated the safety of such antibody treatment for babies whose moms got an RSV vaccine while pregnant, researchers reported Sunday in Atlanta at IDWeek, the joint annual meeting of America’s top infectious disease professional societies.
“Our research reassures new parents that all methods of immunization for RSV are safe and provide high antibody levels to infants, which is especially important as the United States moves into its wave of seasonal respiratory illnesses,” said researcher Dr. Christina Rostad, director of the Emory Children’s Center Vaccine Research Clinic in Atlanta.
“The findings add to the large body of evidence that immunizations to prevent RSV are safe and effective,” she added in a news release.
Nirsevimab is recommended for all babies younger than 8 months of age whose moms didn’t get an RSV vaccine during pregnancy, according to the U.S. Centers for Disease Control and Prevention.
For the study, researchers examined 181 mother/infant pairs from eight hospitals across the United States. The pairs evenly represented three different approaches to RSV prevention:
Vaccination against RSV during pregnancy, which provides antibodies to the developing fetus.
Maternal vaccination combined with the antibody jab three months after birth.
The antibody jab alone for baby, with no vaccination during pregnancy.
Babies in all groups had high antibody levels against RSV, researchers found.
In addition, the babies who got both maternal vaccination and the RSV jab had no serious adverse effects.
The study showed a huge impact from the antibody shot for babies whose moms weren’t vaccinated.
Their RSV protection increased by 25-fold, compared to a more than three-fold increase among those given the jab whose moms were also vaccinated.
The study is ongoing and will test immune durability among moms and babies for one year. Researchers also will test antibody levels found in mothers’ breast milk.
Findings published in Pediatrics in June found that about 2 in 5 (43%) of babies got a nirsevimab injection during the 2023-24 cold and flu season. This was the first season the jab was available following its approval by the U.S. Food and Drug Administration (FDA).
In the Pediatrics study, more than two-thirds of mothers (68%) did not get an RSV vaccine during pregnancy. Overall, about 28% of infants went without any immunization against RSV, either by their moms during pregnancy or an antibody shot afterward.
IDWeek is the joint annual meeting of the Infectious Diseases Society of America, the Society for Healthcare Epidemiology of America, the HIV Medicine Association, the Pediatric Infectious Diseases Society and the Society of Infectious Diseases Pharmacists.
Findings presented at medical meetings should be considered preliminary until published in a peer-reviewed journal.
More information
The U.S. Centers for Disease Control and Prevention has more about RSV.
SOURCE: IDWeek, news release, Oct. 19, 2025
