Vaccinating expectant mothers against RSV reduces hospital admissions in young infants by at least 80 per cent, according to a major study of nearly 300,000 babies in England. 

The research – the largest real world analysis of maternal RSV vaccinations – tracked the electronic health records of 289,399 infants born in England in the year after September 2024, when the rollout of RSV shots for pregnant women began. 

Researchers compared the rates of RSV-related hospitalisations among babies whose mothers did and did not receive an immunisation. Overall, they found that vaccinating expectant mothers at least two weeks before childbirth reduced the risk of hospitalisation by 81.3 per cent. 

Timing mattered: if the vaccine was administered four weeks ahead of birth protection rose to 85 per cent, as there is more time to boost the immune system and pass antibodies to the baby through the placenta. If the shot was administered 10 days before childbirth, protection dropped to 55 per cent – any sooner and the effect was negligible. 

“We’re able to say it’s definitively really good protection against hospitalisation, against being so sick that you need to be admitted for things like oxygen and feeding support,” said Dr Conall Watson,  a consultant epidemiologist at the UK Health Security Agency (UKHSA) and national programme lead for RSV. 

“The size of the analysis also means that we have been able to confirm strong protection in preterm infants, as long as there is a two week gap between vaccination and birth,” he told the Telegraph, adding that the study is 40 times bigger than previous clinical trials. 

RSV, or respiratory syncytial virus, is a common virus that can cause severe respiratory illness, including bronchiolitis and pneumonia, especially in infants and young children. 

According to the World Health Organization, 3.6 million children under five are hospitalised every year because of RSV, while 100,000 die. The vast majority of these fatalities are in low and middle income countries, where access to intensive care is more limited. 

Dr Watson said the results of the UKHSA study present a “huge opportunity” to prevent death in these countries, by stopping hospitalisations from happening in the first place. 

In England, maternal RSV vaccine uptake is rising – from 55 per cent during the study period, to 64.1 per cent in November 2025. Dr Watson said the latest results should “give great reassurance to pregnant women that vaccination is absolutely the right thing to do to protect their baby”. 

The study was presented on Saturday at the European Society of Clinical Microbiology and Infectious Diseases. Researchers said they hope to next assess how protection changes later in infancy.

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