RSV Vaccine in Pregnancy

For adults, respiratory syncytial virus usually feels like a cold. Small babies are different: their airways are tiny, and RSV can inflame the smallest of them — bronchiolitis — or cause pneumonia. A typical UK season starts in October, peaks in December and declines by March.

The burden is real: roughly 33,500 hospital admissions a year in UK children under five, and JCVI figures for babies under one of around 270,000 symptomatic infections, 20,000 admissions and 20 to 30 deaths a year. The riskiest period is a baby's first six months — exactly the window a maternal vaccine covers.

That is why, on JCVI advice, the UK launched a national maternal RSV vaccination programme in late summer 2024 — Scotland from 12 August, the rest of the UK from 1 September: a single dose of Pfizer's bivalent RSVpreF vaccine, Abrysvo, offered from 28 weeks.

The key trial is MATISSE, an international placebo-controlled study of 7,386 pregnant women. Efficacy against severe medically attended RSV lower respiratory tract illness in their babies was 81.8% (99.5% CI 40.6–96.3) within 90 days of birth and 69.4% (CI 44.3–84.1) within 180 days. In absolute terms, 57 of 3,495 infants of vaccinated mothers developed RSV lower respiratory tract disease of any severity in the first six months, versus 117 of 3,480 with placebo.

Then the NHS rolled it out, and the real-world answer matched. The BronchStart study across 30 UK hospitals in the first season (September 2024 to January 2025) compared 391 babies admitted with RSV against 146 RSV-negative controls: adjusted effectiveness against RSV hospitalisation was 58% (95% CI 28–75) overall, and 72% (95% CI 48–85) with vaccination more than 14 days before birth — published in The Lancet Child & Adolescent Health in 2025.

The vaccine does not make RSV impossible — what it does, in trial and NHS practice alike, is make severe illness and hospital admission much less likely in the months your baby is smallest.

The vaccine is offered from 28 weeks — ideally in week 28 or soon after — and you stay eligible up to delivery. Earlier is better: antibodies need time to build and cross the placenta, protection was stronger when vaccination came more than 14 days before birth, and transfer may be lower after week 36. Prompt vaccination at 28 weeks also means a baby who arrives prematurely has had weeks of transfer rather than none.

Unlike the flu jab it is given year-round, because babies are born in every month and RSV returns every winter. The NHS confirms it can be given at the same appointment as your other pregnancy vaccinations, though the schedule usually separates them — the whooping cough vaccine comes earlier in pregnancy, the flu vaccine in flu season.

Start with scale: over 12 million doses worldwide, more than 1.5 million in the UK since September 2024, with a good safety profile in surveillance. The common side effects are ordinary — injection-site pain (41% in the trial), headache (31%), muscle aches (27%) — mostly mild and settling within days. As a non-live vaccine it cannot cause RSV infection.

Now the question you may have read about: premature birth. In 2022 GSK abandoned its own maternal RSV vaccine after a preterm-birth imbalance in its trials, so regulators examined Abrysvo on exactly this point. In MATISSE, preterm birth occurred in 5.7% of the vaccine group versus 4.7% with placebo — relative risk 1.20 (95% CI 0.98–1.46), not statistically significant. The published 2025 analysis found the imbalance came entirely from non-high-income trial countries; in high-income countries rates were identical, 5.0% in both arms (RR 1.00, 95% CI 0.79–1.28).

The JCVI weighed exactly this evidence before recommending the UK programme, and was reassured that the high-income-country data showed no clear preterm-birth signal. UK surveillance agrees: preterm birth in the month after immunisation ran at 2.1% in vaccinated women versus 1.9% unvaccinated — statistically equivalent. Guillain-Barré syndrome has been reported in vaccinated older adults (10 to 25 cases per million doses), with no evidence of increased risk in pregnant women.

And what is not yet known: this vaccine is newer than the flu and whooping cough jabs — UK experience spans two winters, not a decade — so UKHSA and MHRA monitoring continues. No serious signal has emerged in pregnant women, and the NHS's judgement is that vaccination is much safer than the risk of your baby getting RSV.