Largest study yet shows RSV vaccine in pregnancy cuts babies’ hospital risk by 80%
Biggest real-world analysis finds babies are far less likely to be hospitalised with respiratory syncytial virus when mothers were vaccinated at least two weeks before delivery.
- 20 April 2026
- 6 min read
- by Linda Geddes
At a glance
- The study analysed real-world data from nearly 290,000 infants born in England between September 2024 and March 2025.
- It found that maternal vaccination against RSV cut babies’ risk of hospitalisation with RSV-related illness by 81.3% when given at least two weeks before birth. Protection rose to almost 85% when vaccination took place at least four weeks before delivery.
- For preterm infants, who are at greater risk of severe RSV infection, maternal vaccination cut babies’ risk of hospitalisation by 69.4% when mothers were vaccinated at least 14 days before birth.
The largest real-world study to date of maternal vaccination against respiratory syncytial virus (RSV) has confirmed that the vaccine is highly effective, reducing the risk of hospitalisation in young babies by more than 80% when given at least two weeks before birth.
Protection rose to almost 85% when the vaccine was given at least four weeks before delivery.
Researchers also found strong protection in preterm babies, who are among the most vulnerable to severe RSV infection.
What is RSV and why does it cause hospitalisations?
RSV is a leading cause of lower respiratory tract infections such as bronchiolitis and pneumonia in children under five.
Almost all babies are infected by their second birthday and, while most develop only mild symptoms such as a runny nose, sore throat, headache, fatigue and fever, some become seriously unwell, with infants younger than six months at particularly high risk of severe illness and death.
The risk is particularly high in lower-income countries. Each year, the virus causes more than 3.6 million hospitalisations and around 100,000 deaths among children under five. Some 97% of those deaths occur in low- and middle-income countries, where access to supportive medical care is limited. RSV-related lower respiratory tract infections in early life have also been linked to longer-term health problems, including repeated hospital admissions for lung infections during infancy, wheezing, asthma and poorer lung health later in childhood.
The virus can also cause severe illness in elderly people and those with underlying illnesses.
What vaccines are available to protect babies against RSV?
There are currently three licensed immunisation products designed to protect young infants from RSV in early life.
Two aren’t vaccines in the traditional sense, but ready-made (monoclonal) antibodies that provide immediate protection to the baby through their first RSV season.
There is also a maternal RSV vaccine known as the Bivalent Prefusion F (Abrysvo) vaccine, which is given during the later stages of pregnancy and stimulates the mother’s immune system to produce antibodies that cross the placenta and protect the newborn during their first months of life. This maternal vaccine is the subject of the latest study.
How effective is the maternal RSV vaccine?
The maternal RSV vaccine received WHO prequalification in 2025, a key criterion for financial support from Gavi, the Vaccine Alliance and for procurement by UN agencies such as UNICEF, after clinical trials showed it to be safe and effective.
A multi-dose vial presentation of the same vaccine is expected to receive WHO prequalification and become eligible for Gavi support in 2027.
A Pfizer-sponsored phase 3 trial conducted in 18 countries over four RSV seasons found that the vaccine reduced the risk of babies being admitted to hospital with RSV by 68% during their first three months of life and by 57% within six months of birth.
It also reduced the risk of severe RSV-related outcomes, including low blood oxygen, the need for mechanical ventilation or admission to intensive care, by 82% within three months and 69% within six months after birth.
Whereas clinical trials measure vaccine efficacy under ideal conditions, the latest study used real-world data from 289,399 infants born in England between September 2024 and March 2025 – representing around 90% of births in England during this period – to estimate its effectiveness in everyday use.
The research, presented at ESCMID Global 2026 this week, found that maternal RSV vaccination reduced the risk of infants being hospitalised with RSV by 81.3% when given at least 14 days before birth, rising to almost 85% when administered at least four weeks before delivery.
In total, 4,594 RSV-associated hospitalisations were recorded, with babies born to unvaccinated mothers accounting for 87.2% of admissions despite making up just 55% of the study group.
“As the largest study to date examining the impact of this vaccine on infant hospitalisation, these findings provide robust evidence that vaccination offers substantial protection against severe illness in young infants,” said Matt Wilson, an epidemiologist for the UK Health Security Agency (UKHSA) and the study’s lead author.
When should women get the RSV vaccine?
WHO’s SAGE advisory group recommends the maternal RSV vaccine during the third trimester of pregnancy to maximise antibody transfer to the baby before birth. This aligns with the study’s finding that protection was strongest when the vaccine was given earlier.
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“While at least two weeks are typically needed for optimal protection, infants born 10 to 13 days after vaccination had around 50% fewer hospital admissions compared with those whose mothers were unvaccinated, whereas no reduction was seen when vaccination occurred less than ten days before birth,” said Wilson.
“This reinforces the importance of vaccinating as early as possible within the recommended window, while also showing that even when given later in pregnancy, some protection is still possible from around ten days before birth.”
How does the vaccine help preterm babies?
Preterm infants are among those at greatest risk of severe RSV infection, making maternal vaccination particularly important for this group. The study found that vaccine effectiveness against hospitalisation in preterm infants was 69.4% when mothers were vaccinated at least 14 days before birth.
These findings suggest timing is especially important for pregnancies at risk of early delivery, Wilson said: “With sufficient time between vaccination and birth, we saw good levels of protection in these babies. Giving the vaccination early in the third trimester, as recommended by the World Health Organization, could protect most preterm infants.”
What happens next for global RSV vaccination programmes?
While the maternal RSV vaccine has already been approved and introduced in many higher- and upper-middle-income countries, global roll-out is at an early stage.
In 2025, the Gavi Board approved the inclusion of the multi-dose vial presentation of the maternal vaccine into its portfolio, and began with its partners designing a programme to support the vaccine’s introduction in lower-income countries, including country planning and co-ordination with health agencies. Once that phase is complete, they plan to work with governments and health organisations to help deliver effective roll-outs, with a focus on reaching communities most at risk.
Wilson also highlighted the vaccine’s potential global impact: “While survival from RSV bronchiolitis and pneumonia is high in high-income countries, it remains a major cause of infant mortality in low- and middle-income countries,” he said.
“These findings underscore the potential benefits of wider rollout of maternal RSV vaccination globally in line with the World Health Organization’s recommendations.”
