Major UK clinical trial finds surfactant therapy ineffective for severe bronchiolitis

A major UK-led clinical trial has found that a treatment commonly used to help premature babies breathe offers no benefit for infants on life support with severe bronchiolitis - a seasonal viral illness that hospitalizes thousands of babies each year.

Funded by a partnership between the UK's UKRI Medical Research Council (MRC) and National Institute for Health and Care Research (NIHR), and by Chiesi Farmaceutici SpA, Italy, the Bronchiolitis Endotracheal Surfactant Study (BESS) trial is the largest-ever randomized study of surfactant for bronchiolitis.

The results are published today (21 March 2026) in The Lancet Respiratory Medicine.

Bronchiolitis occurs when a virus-most commonly respiratory syncytial virus (RSV)-infects a baby's lungs. There is currently no specific treatment for RSV infection, and the illness can be especially severe in premature and newborn infants. Babies with bronchiolitis have reduced levels of surfactant in their lungs, a condition similar to that seen in babies born prematurely. Because surfactant is routinely used to help premature infants breathe more easily, the study team set out to determine whether this therapy could also benefit babies hospitalized with bronchiolitis.

 The study ran across 15 children's hospitals in England, Scotland, and Northern Ireland and involved 232 critically ill babies. However, surfactant did not reduce the time they needed to be on a ventilator (life-support breathing machine).

Professor Calum Semple OBE, the study's lead from the University of Liverpool and Alder Hey Children's NHS Foundation Trust, said: "The treatment was safe, but it didn't make any difference to how long babies stayed on ventilators. We had hoped that surfactant might speed up recovery for these very sick babies, but the evidence doesn't support this."

Bronchiolitis - most often caused by RSV - is the leading reason why babies are admitted to hospital in the UK during winter. It typically affects babies under one year old and can be especially severe in those born prematurely. While most of the twenty-five thousand babies admitted will recover with oxygen and fluids, around a thousand of the most unwell require intensive care and a ventilator to support their breathing. Currently, there is no other treatment for bronchiolitis, but a vaccine is now being offered to Mum-to-be in the last months of pregnancy.

The BESS trial was designed to give families and clinicians clear answers. It ran over six winter seasons from 2019 to 2024.

While we continue to research better ways to care for these sick babies, I urge Mums-to-be to accept the offer of the RSV vaccine during pregnancy, which will protect their newborn babies from severe bronchiolitis."

Calum Semple, University of Liverpool

The researchers emphasize that surfactant therapy remains essential for premature newborn babies and advocate for further studies to explore targeted treatments for bronchiolitis.