Immunisation with the long-acting monoclonal antibody nirsevimab may provide stronger protection against hospitalisations for respiratory syncytial virus (RSV) in infants than maternal RSV vaccination during pregnancy, though the difference appears to disappear when maternal vaccination occurs at least eight weeks before delivery, reports CIDRAP News.
That’s according to a large French study published recently in The Lancet Child & Adolescent Health, in which a team led by researchers at Universite Paris Cite and Universite Sorbonne Paris Nord compared infant immunisation with nirsevimab shortly after birth with maternal vaccination with the RSV prefusion F (RSVpreF, Abrysvo) vaccine during pregnancy.
Lower odds of hospital stay
For the population-based retrospective cohort study, the team analysed health data from 164 140 infants born from September 2024 to February 2025. Of those newborns, 103 062 received nirsevimab after birth, and 61 078 were born to mothers vaccinated during pregnancy with RSVpreF vaccine. After matching infants by birth date, sex and region, the researchers compared outcomes in 42 098 infants in each group.
At the six-month follow-up, 350 infants (0.83%) in the nirsevimab group were hospitalised for RSV-related lower respiratory tract infection (LRTI), compared with 403 infants (0.96%) in the maternal vaccine group.
That translated to 22% lower odds of RSV-related hospitalisation for the infants in the nirsevimab group (odds ratio [OR], 0.78).
But the timing of maternal vaccination appeared to matter. When RSVpreF vaccination occurred at least eight weeks before delivery, researchers found no statistically significant difference between the two approaches (OR, 1.01). Similarly, no significant difference was seen when maternal vaccination occurred between 28 and 31 weeks of gestation.
“We found that the longer the interval between maternal RSVpreF vaccination and delivery, the smaller the difference between the two products,” write the researchers.
“Overall, these findings highlight that the comparative effectiveness of nirsevimab at birth versus maternal RSVpreF vaccine is strongly influenced by the timing of maternal vaccination during pregnancy and suggest that early maternal vaccination during pregnancy could optimise its effectiveness.”
RSV a leading cause of childhood illness, death
RSV is the leading cause of LRTIs in children under five, and remains a major cause of illness and death worldwide. Infants in the first six months of life face the greatest risk, accounting for 1.4m hospitalisations and 45 000 deaths annually.
The study had some limitations. The research was done during a single RSV season in France, so the findings may not be generalisable to other seasons with different circulating strains.
The researchers also used medical billing and diagnostic codes to identify RSV-related infections, which means some cases could have been categorised incorrectly.
Still, say the authors, the findings add to the body of evidence suggesting that infant immunisation with nirsevimab may be slightly superior to maternal RSVpreF vaccination in protecting newborns against RSV.
The data also suggest that, when maternal vaccination happens at least eight weeks before delivery, it may be similarly effective in reducing hospitalisations. “These results could help policy makers optimise public health decisions to maximise RSV prevention in infants,” the authors conclude.
Study details
Effectiveness of nirsevimab immunisation after birth versus RSVpreF maternal vaccination in preventing RSV-related hospitalisations in infants: a population-based retrospective cohort study
Zaba Valtuille, Inès Fafi, Florentia Kaguelidou et al.
Summary
Background
Maternal respiratory syncytial virus (RSV) prefusion F (RSVpreF) vaccine and nirsevimab immunisation are two products recently implemented to reduce RSV-related lower respiratory tract infection (LRTI) in infants (nirsevimab since 2023 and RSVpreF since 2024). We aimed to assess the effectiveness of nirsevimab immunisation at birth versus RSVpreF maternal vaccination in preventing RSV-related LRTI hospitalisations in children before age 6 months.
Methods
This population-based retrospective cohort study used data from the French National Health Data System and included all children born across metropolitan France between 1 September 2024, and 28 February 2025, who either received nirsevimab at birth (nirsevimab group) or whose mothers received RSVpreF vaccine between 28 weeks and 36 weeks of gestation (RSVpreF group). Children who received neither immunisation, those born from mothers not aged 13–50 years, and those who could not be linked to their mother in the database were not included. Children were matched on birth date, region of birth, and sex. The primary outcome was RSV-related LRTI hospitalisation at six months. Propensity score analysis adjusted for baseline characteristics. Secondary analyses were performed, notably assessing the influence of the timing of RSVpreF maternal vaccination during pregnancy on the main outcome.
Findings
During the study period, 164 140 children were included, of whom 83 978 (51·2%) were male and 80 162 (48·8%) female; mean gestation at birth was 39·4 weeks (SD 1·2), 103 062 (62·8%) received nirsevimab after birth, and 61 078 (37·2%) were born to mothers vaccinated with RSVpreF. 42 098 children from each group were matched. During the 6-month follow-up, 753 RSV-related LRTI hospitalisations occurred: 350 (0·83%) of 42 098 infants in the nirsevimab immunisation group and 403 (0·96%) of 42 098 infants in the RSVpreF vaccine group. After adjustment, nirsevimab was associated with a 22% reduction in the odds of RSV-related LRTI hospitalisation compared with RSVpreF vaccination (OR 0·78 [95% CI 0·70–0·86]). Although the odds of RSV-related LRTI hospitalisation were lower with nirsevimab than with RSVpreF vaccination when RSVpreF vaccination was given between 2 weeks and less than 4 weeks (0·45 [0·32–0·63]), between 4 weeks and less than 6 weeks (0·80 [0·68–0·95]), and between 6 weeks and less than 8 weeks before delivery (0·80 [0·60–0·99]), there was no difference between nirsevimab and RSVpreF given 8 weeks or more before delivery (1·01 [0·77–1·32]).
Interpretation
Compared with RSVpreF maternal vaccine, nirsevimab at birth was associated with a reduction in the odds of RSV-related LRTI hospitalisation at age 6 months in the 2024–25 RSV season. Exploratory secondary analyses suggest that an interval of at least 8 weeks between RSVpreF vaccination and delivery could provide protection not statistically different from nirsevimab at birth. These findings can guide future public health decisions.
See more from MedicalBrief archives:
Jab could slash RSV babies’ hospital admissions by 80% – global study
Respiratory virus killing 100,000 children a year – systemic analysis