Researchers found the respiratory syncytial virus (RSV) vaccine, introduced across the UK in late summer 2024, led to a 72 percent reduction in babies hospitalized with the virus if mothers were vaccinated.

The findings are the first to show the real-world effectiveness of the vaccine in pregnant women in the UK.

Uptake of the jab among pregnant women could help to limit the number of sick babies each winter, reducing hospital pressures, experts say.

RSV is a common virus that causes coughs and colds but can lead to a severe lung infection called bronchiolitis, which can be dangerous in babies, with some requiring admission to intensive care. The virus is the main infectious cause of hospitalization for babies in the UK and globally.

Receiving the vaccine during pregnancy helps to protect both mother and baby. Antibodies - proteins which help to prevent the virus causing severe infection - produced by the mother in response to the vaccine are passed to the fetus, providing protection from severe RSV for the first six months after birth.

The research team, led by the Universities of Edinburgh and Leicester, recruited 537 babies across England and Scotland who had been admitted to hospital with severe respiratory disease in the winter of 2024-2025, the first season of vaccine implementation. 391 of the babies tested positive for RSV.

Mothers of babies who did not have RSV were two times more likely to have received the vaccine before delivery than the mothers of RSV-positive babies - 41 percent compared with 19 percent.

Receiving the vaccine more than 14 days before delivery offered a higher protective effect, with a 72 percent reduction in hospital admissions compared with 58 percent for infants whose mothers were vaccinated at any time before delivery.

Experts recommend getting vaccinated as soon as possible from 28 weeks of pregnancy to provide the best protection, as this allows more time for the mother to generate and pass on protective antibodies to the baby, but the jab can be given up to birth.

Previous research has found that only half of expectant mothers in England and Scotland are currently receiving the RSV vaccine, despite its high success at preventing serious illness.

The findings highlight the importance of raising awareness of the availability and effectiveness of the new vaccine to help protect babies, experts say.

The study is published in the journal The Lancet Child and Adolescent Health. The research collaboration also included the Universities of Bristol, Oxford, Queen's University Belfast, UCL and Imperial College London and 30 hospitals across England and Scotland.

The study was funded by the Innovative Medicines Initiative (IMI) Respiratory Syncytial Virus Consortium in Europe (RESCEU), the Wellcome Trust and National Institute for Health and Care Research (NIHR) Health Protection Research Unit in Respiratory Infections, Imperial College London.

Dr Thomas Williams, study lead from the University of Edinburgh's Institute for Regeneration and Repair, and Paediatric Consultant at the Royal Hospital for Children and Young People in Edinburgh, said: "With the availability of an effective RSV vaccine shown to significantly reduce the risk of hospitalization in young infants in the UK, there is an excellent opportunity for pregnant women to get vaccinated and protect themselves and their infants from RSV bronchiolitis this coming winter."

Professor Damian Roland from the Leicester Hospitals and University and Consultant in Paediatric Emergency Medicine, said: "Our work highlights the value of vaccination and in keeping with the treatment to prevention principle of the NHS 10 Year plan we would ask all health care systems to consider how they will optimize the roll out of RSV vaccination for mothers."