Maternal RSV Vaccination Reduces Infant Hospitalisation Risk by Over 80%, UK Study Finds
Receiving a respiratory syncytial virus (RSV) vaccine during pregnancy significantly lowers the risk of severe illness in newborns, with a major UK study showing more than 80% protection against hospitalisation when given at least two weeks before birth. The findings, presented by the UK Health Security Agency (UKHSA) at the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) Global Congress, reinforce growing evidence that maternal immunisation is a powerful tool to protect infants too young to be vaccinated themselves.
Understanding RSV and Its Threat to Infants
Respiratory syncytial virus is a common respiratory pathogen that typically causes mild, cold-like symptoms in older children and adults. However, in infants—especially those under six months—it can lead to bronchiolitis and pneumonia, often requiring hospitalisation. RSV is the leading cause of lower respiratory tract infection in babies worldwide, resulting in tens of thousands of hospital admissions each year in the UK alone.
Because infants’ immune systems are not fully developed, they cannot mount a strong response to traditional vaccines. This has led researchers to focus on maternal vaccination as a strategy: by vaccinating the mother during pregnancy, protective antibodies are transferred across the placenta, offering the newborn passive immunity during the vulnerable first months of life.
Key Findings from the UKHSA Study
The UKHSA analysis evaluated data from pregnant individuals who received the RSV vaccine (Abrysvo, developed by Pfizer) and compared hospitalisation rates among their infants to those born to unvaccinated mothers. The study found that maternal vaccination administered at least two weeks prior to delivery was associated with an over 80% reduction in the risk of RSV-related hospitalisation in infants under three months of age.
Protection was strongest when the vaccine was given later in pregnancy—ideally between 28 and 36 weeks gestation—allowing sufficient time for antibody transfer. Infants born to mothers vaccinated less than two weeks before birth showed significantly lower levels of protection, underscoring the importance of timing.
These results align with earlier clinical trial data that led to regulatory approval of Abrysvo for use in pregnancy by the European Medicines Agency (EMA) and the U.S. Food and Drug Administration (FDA) in 2023.
How Maternal RSV Vaccination Works
The Abrysvo vaccine contains a stabilized version of the RSV fusion (F) protein, which the virus uses to enter human cells. By presenting this antigen, the vaccine prompts the mother’s immune system to produce neutralizing antibodies. These immunoglobulin G (IgG) antibodies actively cross the placenta starting in the second trimester, with peak transfer occurring in the final weeks of pregnancy.
newborns are born with high levels of RSV-specific antibodies that can block viral entry and replication, providing critical protection during the period when they are most susceptible to severe disease.
Safety Profile and Recommendations
Large-scale studies involving tens of thousands of pregnant individuals have shown that the RSV vaccine has a favorable safety profile. The most commonly reported side effects are mild and include pain at the injection site, headache, muscle pain, and nausea—similar to those seen with other routine prenatal vaccines like Tdap and influenza.
No increase in adverse pregnancy outcomes, such as preterm birth or low birth weight, has been linked to the vaccine in current evidence. The World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) now recommend maternal RSV vaccination as part of standard prenatal care in regions where the vaccine is available.
In the UK, the Joint Committee on Vaccination and Immunisation (JCVI) has advised a phased rollout of the maternal RSV vaccine through the National Health Service (NHS), with implementation expected to begin in late 2024 or early 2025.
Broader Implications for Public Health
Maternal RSV vaccination represents a shift toward protecting infants through indirect immunization—a strategy already proven effective for diseases like tetanus, diphtheria, and pertussis via the Tdap vaccine. By preventing severe RSV cases in early infancy, this approach could reduce strain on pediatric hospitals during winter months, when RSV typically circulates alongside influenza and other respiratory viruses.
Experts note that combining maternal vaccination with emerging options like long-acting monoclonal antibodies (e.g., nirsevimab) for infants may offer layered protection in the future. However, maternal immunisation remains advantageous due to its scalability, cost-effectiveness, and ability to protect babies from birth.
Frequently Asked Questions
When should pregnant individuals get the RSV vaccine?
The optimal window for RSV vaccination during pregnancy is between 28 and 36 weeks gestation, as recommended by the CDC and WHO. This timing maximises antibody transfer to the fetus while ensuring the mother mounts a strong immune response.
Can the RSV vaccine be given at the same time as other vaccines?
Yes. The RSV vaccine can be administered concurrently with other routinely recommended prenatal vaccines, such as the flu shot and Tdap booster, without reducing effectiveness or increasing risk.
How long does protection last for the infant?
Antibodies transferred from the mother provide peak protection in the first 60 to 90 days of life, gradually declining over the first six months. This covers the period of highest vulnerability to severe RSV disease.
Is the vaccine safe if I have a high-risk pregnancy?
Current data show no safety concerns for individuals with common high-risk pregnancies, including those with gestational diabetes or hypertension. However, individuals should consult their obstetrician or midwife to discuss their specific circumstances.
Will I need an RSV vaccine in every pregnancy?
Yes. Like the flu and Tdap vaccines, maternal RSV vaccination is recommended during each pregnancy to ensure optimal antibody transfer to each newborn.
Key Takeaways
- Maternal RSV vaccination reduces the risk of infant hospitalisation by over 80% when given at least two weeks before birth.
- The vaccine works by transferring protective antibodies across the placenta, offering newborns passive immunity.
- Administration between 28 and 36 weeks of pregnancy provides the best protection.
- The vaccine has a strong safety profile, with side effects similar to other prenatal immunisations.
- Public health agencies in the UK, EU, and US now recommend RSV vaccination as part of routine prenatal care.
Looking Ahead
As countries prepare to integrate maternal RSV vaccination into national immunisation programmes, ongoing surveillance will be critical to monitor real-world effectiveness, duration of protection, and impact on healthcare systems. The success of this initiative could pave the way for similar maternal vaccine strategies targeting other neonatal pathogens, such as group B streptococcus or cytomegalovirus.
For expectant parents, the message is clear: getting vaccinated against RSV during pregnancy is one of the most effective steps available today to protect their newborn from a potentially serious respiratory illness in the first months of life.