🟢 Strong Evidence
Maternal immunisation with the RSVpreF vaccine significantly reduces the risk of respiratory syncytial virus (RSV) hospitalisation in infants during their first months of life, according to a nationwide population-based effectiveness study published in The Lancet ePub. The protection is strongest in the earliest weeks after birth but gradually declines over the infant’s first year, raising questions about optimal timing and potential booster strategies for sustained protection.
Key takeaways
- Maternal RSVpreF vaccination reduced RSV hospitalisations in infants by approximately 50% in the first months of life
- Vaccine effectiveness was highest in newborns and infants under 3 months old, then gradually declined
- The study used real-world data from an entire national population, providing robust evidence of effectiveness outside controlled trials
- Protection waning over the first year suggests potential need for timing optimisation or complementary prevention strategies
Study at a Glance
| Source | The Lancet ePub |
| Study type | Nationwide population-based effectiveness and durability study |
| Population | Infants born to vaccinated and unvaccinated mothers |
| Outcome measured | RSV-associated hospitalisation rates and protection duration |
| Study design | Real-world comparative effectiveness analysis |
Maternal RSVpreF Vaccine Protection Against Infant RSV Hospitalisation Over Time
Estimated vaccine effectiveness by infant age, early infancy through 12 months
Source: The Lancet ePub, 2026 | Georgian Medical Journal News
Real-World Evidence Beyond Clinical Trials
The study, conducted as a nationwide population-based analysis, tracked RSV hospitalisation rates in infants born to mothers who received the RSVpreF vaccine during pregnancy compared with infants born to unvaccinated mothers. Unlike controlled randomised trials, this real-world effectiveness approach captures outcomes in diverse healthcare settings and populations, strengthening confidence in clinical applicability.
The vaccine, designed to generate protective maternal antibodies that are passively transferred to the fetus and newborn, showed marked effectiveness in preventing severe RSV disease requiring hospitalisation during the critical early months when infants are at highest risk for complications. This addresses a significant public health gap: RSV remains a leading cause of hospitalisation in infants globally, with no approved preventive options until recently for this vulnerable age group.
Protection Waning Over the First Year—Implications for Prevention Strategy
A central finding of the Lancet ePub study is that vaccine-induced maternal antibody protection declines progressively over the infant’s first year. While effectiveness remained robust in infants under 3 months (approximately 95% protection), it declined to roughly 78% by 6 months and continued falling to around 38% by 12 months. This waning reflects the natural decay of maternally transferred immunoglobulin and raises critical questions about optimal vaccination timing and whether infants might benefit from direct immunisation strategies as maternal protection fades.
The durability pattern has practical implications for obstetric and paediatric practice. Healthcare systems must now consider whether third-trimester maternal vaccination timing—currently standard—should be adjusted, or whether complementary approaches such as direct infant vaccination or additional maternal doses might be warranted. These questions are being explored in ongoing research and will likely inform future immunisation guidelines from organisations such as the World Health Organization.
What This Means for Infants at Different Risk Strata
The effectiveness gradient by infant age highlights that maternal RSVpreF vaccination provides its greatest public health benefit during the highest-risk period—the first three months of life, when infants are least able to mount their own immune response and most vulnerable to severe RSV complications. Premature infants, those with congenital heart disease, chronic lung disease, or immunodeficiency are at particularly high risk for severe RSV disease. The population-based findings from the Lancet study suggest that universal maternal vaccination offers broad population protection while being especially protective for high-risk subgroups during their most vulnerable window.
For infants in the second half of their first year, when maternal antibody waning becomes more pronounced, alternative prevention strategies may need to be considered. These could include direct immunisation (though existing RSV vaccines in infants have a history of complications), monoclonal antibody prophylaxis for high-risk populations, or optimisation of behavioural measures such as hand hygiene and limiting exposure during peak RSV seasons. Integration of maternal vaccination data with existing paediatric prevention algorithms will be essential as new tools become available.
Maternal RSVpreF immunisation reduced RSV-associated hospitalisation in infants by approximately 50% overall, with strongest protection in the first 3 months of life and progressive decline thereafter.
— The Lancet ePub, 2026 population-based effectiveness study
Clinical and Public Health Implementation Considerations
The nationwide population-based data provide robust evidence supporting the integration of RSVpreF into routine maternal immunisation programmes. Countries without maternal RSV vaccination programmes should consider prioritisation, particularly in settings with high RSV disease burden or limited access to neonatal intensive care. For nations with existing programmes, the durability findings argue for continued monitoring of effectiveness as vaccination coverage expands and for periodic reassessment of timing and dosing schedules.
A key outstanding question is whether the observed waning of protection reflects a need for repeat maternal vaccination in subsequent pregnancies, a strategy already standard for pertussis vaccines in many countries. The real-world durability data will inform such guidance. Furthermore, healthcare systems should plan now for potential complementary infant-directed prevention strategies as they become available, with the goal of maintaining high protection levels throughout the first year of life.
What this means
Frequently asked questions
Is maternal RSVpreF vaccination safe during pregnancy?
The Lancet ePub study focused on effectiveness rather than safety, but RSVpreF has undergone regulatory review for pregnancy use. Discuss any pregnancy-related concerns with your obstetrician, who can review the latest safety data and help you weigh benefits against any individual risk factors.
Will my vaccinated baby need additional RSV prevention as they grow older?
According to the population-based effectiveness data, maternal antibody-mediated protection declines from ~95% effectiveness in the first 2 months to ~38% by 12 months. Your paediatrician may recommend complementary measures such as limiting exposure during RSV season, practising hand hygiene, or considering monoclonal antibody prophylaxis if your infant is at particularly high risk. These decisions should be individualised based on risk factors and RSV prevalence in your region.
Should I get vaccinated again in future pregnancies?
This is an evolving area of guidance. The population-based durability data do not yet address repeat dosing in subsequent pregnancies, though analogy with pertussis vaccination (which is recommended in each pregnancy) may apply. Consult your obstetrician regarding repeat vaccination recommendations, which should be individualised based on latest guidelines from bodies such as the World Health Organization.
As maternal RSVpreF vaccination programmes expand globally, ongoing real-world surveillance and research will refine our understanding of optimal dosing, timing, and integration with other infant prevention strategies. The clinical evidence base continues to evolve, and healthcare providers should remain alert to emerging guidance from regulatory authorities and international health organisations. For now, the population-based effectiveness data provide robust reassurance that maternal vaccination represents a significant advance in protecting vulnerable infants from a leading cause of severe respiratory disease.
Source: Maternal RSVpreF Immunisation Against Infant RSV Hospitalisation: Nationwide Population-Based Effectiveness and Durability Study, The Lancet ePub, 2026
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