Six recent studies conclude that maternal respiratory syncytial virus (RSV) vaccination and the long-acting monoclonal antibody nirsevimab for infants help protect mothers and their infants from infection and poor outcomes.
RSV is a common virus that can cause severe lower respiratory tract infections (LRTIs) such as bronchiolitis and pneumonia in infants and young children.
Safe, immunogenic to give both immunizations together
Given alone or together, maternal RSVpreF (Abrysvo) vaccination and infant immunization with the long-acting RSV monoclonal antibody nirsevimab (Beyfortus) are safe and trigger production of high neutralizing antibody (nAb) levels, interim findings from the first single head-to-head comparison show.
For the phase 4 randomized trial, a team led by Emory University investigators randomly assigned 181 mother-infant pairs at eight US centers to one of four trial arms: maternal RSV vaccine alone, maternal vaccine/infant nirsevimab at birth, maternal RSV vaccine and infant nirsevimab given at 3 months of age, or infant nirsevimab alone at birth, with one year of follow-up.
Most infants do not need protection via both maternal vaccine and infant immunization, although there are certain circumstances when the benefit of administering both products should be considered.
Blood and optional breast milk samples were analyzed, and infants underwent a physical exam. All infants were full-term. The interim results of the open-label trial, published this week in Pediatrics, cover the period from September 2024 to May 2025, including four-month infant follow-up.
To prevent severe RSV in infants, the American Academy of Pediatrics recommends either maternal RSV vaccination or infant immunization with nirsevimab or the recently approved clesrovimab (Enflonsia). “Most infants do not need protection via both maternal vaccine and infant immunization, although there are certain circumstances when the benefit of administering both products should be considered,” the study authors wrote.
The trial demonstrated that both products alone and in combination are safe. No related serious adverse events were seen in mothers or infants with administration of either product alone or in combination. Nirsevimab was well tolerated, and all local and systemic reactions were mild to moderate.
RSVpreF raised maternal nAb concentrations 17.4-fold at delivery, and levels remained steady through three months after delivery. The geometric mean maternal-to-baby transfer ratio of nAbs was higher than 1.3 and comparable in all groups. RSV nAb titers were high in infants at 6 weeks and 3 months of age across groups, with only slight differences in waning.
“Maternal RSV vaccination and infant nirsevimab immunization, administered either alone or sequentially, were safe and provided high RSV-A and -B nAb titers in infants that persisted through 3 months after delivery,” the researchers concluded. “While most infants will not need to receive both products to be protected, our results suggest that maternal RSV vaccination and infant nirsevimab immunization may be safely sequentially administered.”
In a commentary in the same journal, Michael Rajnik, MD, and Martin Ottolini, MD, MEd, both of the Uniformed Services University of the Health Sciences, noted that infants given nirsevimab have similar concentrations of nAbs against both RSV-A and -B by 6 weeks and maintain higher levels at 3 months than those conferred through maternal vaccination alone. “From an immunologic standpoint, this suggests that longer protection will occur if a child receives nirsevimab,” they wrote.
But they cautioned that “though the findings are reassuring, we need to realize that this study is not powered to answer concerns about adverse events, although prelicensure data suggest that both approaches are safe when given individually and no postmarketing research has suggested unusual patterns of adverse events.”
“Additionally, we cannot comment at this time on the children who are scheduled to be born to a mother who was immunized and to then receive sequential nirsevimab at 3 months as that data have not yet been reported,” they added.
Vaccine 82% effective against maternal infection
In related news, a real-world multicenter electronic health record (EHR) study estimates the effectiveness of the RSV vaccine in pregnant women at 82.1% one year after receipt.
Researchers at Nara Prefecture General Medical Center in Japan examined the EHRs of pregnant women in the United States who sought medical care at 28 weeks’ gestation or later and were tested for RSV from September 2023 to February 2026.
Of 2,440 and 17,537 vaccinated and unvaccinated pregnant women, 2,434 in each group were matched. The aim was to evaluate the effectiveness of the vaccine against maternal RSV infection. The findings were published last week in Vaccine.
The preventive effect of RSV vaccination on vaccinated mothers presented in this study indicates a unique additional benefit of maternal RSV vaccination compared with infantile immunization.
Many high-income countries recommend that all infants be protected against RSV through maternal vaccination or infant monoclonal antibody immunization.
“However, their decisions are solely based on an infantile-beneficial perspective, without considering the potential protective impact of maternal vaccination against RSV infection and its associated negative outcomes in pregnant women because of a lack of evidence,” the authors wrote.
After matching, 0.5% and 2.8% of women in the vaccinated and unvaccinated groups had confirmed RSV infection, respectively. The risk ratio (RR) of RSV infection in the vaccinated cohort relative to the unvaccinated cohort was 0.18, corresponding to a VE of 82.1%, at one year. RSV-linked lower respiratory tract infection was diagnosed in 0 and 0.6% of cases in the vaccinated and unvaccinated groups, respectively.
VE in each sensitivity analysis was estimated at 76.5% by excluding rapid antigen testing as a confirmation method, 79.3% after matching only with demographic factors, 75.5% by restricting gestational period to 32 weeks or later, 78.5% with two years between the index date and RSV testing, respectively. VE could not be estimated in the six-month interval between the index date and RSV testing and by season owing to the small number of outcome events.
“The preventive effect of RSV vaccination on vaccinated mothers presented in this study indicates a unique additional benefit of maternal RSV vaccination compared with infantile immunization,” the authors wrote.
“In conclusion, our study showed that RSV vaccination is effective in vaccinated mothers. This indicates an additional benefit of maternal RSV vaccination compared with infantile monoclonal antibodies,” they added.
4 other studies reach similar conclusions
In other recent studies:
- Maternal RSV vaccination slashes the risk of infant hospitalization by 81%, concludes a study conducted by the UK Health Security Agency and presented at last month’s European Society of Clinical Microbiology and Infectious Diseases (ESCMID) Global 2026 meeting in Munich. The researchers analyzed linked national datasets on 289,399 infants born from September 2024 to March 2025, making up about 90% of births in England during this period. In total, 4,594 infants were hospitalized for RSV, and while the infants of unvaccinated mothers made up 55% of the cohort, they accounted for 87.2% of hospitalizations. In contrast, the infants of vaccinated mothers had a much lower risk of hospitalization, with an estimated VE of 81.3% compared with the unvaccinated group.
- A study by researchers from NYU Health + Hospitals/Elmhurst suggests that maternal RSV vaccination or nirsevimab immunization in kids significantly lowers rates of infection and healthcare use and is linked to fewer severe RSV complications in infected infants compared with no vaccination. Maternal vaccine and infant nirsevimab uptake were greater than 65% and 90%, respectively, but the news release didn’t provide VE estimates. The researchers analyzed rates of RSV hospitalization, need for respiratory support, and six-month outcomes in New York in October 2023. The study was presented late last month at the Pediatric Academic Societies 2026 Meeting in Boston.
- Nirsevimab administration was tied to a 79.5% reduction in RSV hospitalizations in high-risk infants with LRTI, with estimated drops of 74.4% among extremely preterm infants and those with congenital heart disease (CHD) and 87.6% in those with congenital heart disease alone, per a case-control study published last month in JAMA Network Open. The Chilean researchers mined the national health registries of all hospitals in the country in 2024 to estimate the effectiveness of nirsevimab in 177 hospitalized high-risk infants and an unhospitalized control group of 708 matched peers. Nirsevimab was linked to a reduced risk of RSV LRTI hospitalization of 84.3% in at-risk infants, 85.1% in those with both extreme prematurity and CHD, and 96.3% in those with CHD.
- Nirsevimab and maternal RSV vaccination were associated with an estimated a 43.0% relative decrease in the population rate of RSV hospitalization and emergency department (ED) visits for children 7 months or younger beyond that also seen in children 8 to 24 months old in the 2024-25 respiratory virus season (the second season of product availability). Researchers from the Washington State Department of Health and the Centers for Disease Control and Prevention published the difference-in-differences study last month in JAMA Network Open. “Results support continued use of these products in the state,” they wrote.
