Monoclonal Antibody Approved To Prevent RSV

MSD announced that the UK’s Medicines & Healthcare Products Regulatory Agency (MHRA) granted Marketing Authorisation to ENFLONSIA^®  (clesrovimab) indicated for the prevention of respiratory syncytial virus (RSV) lower respiratory tract disease in neonates and infants during their first RSV season.i

Before the RSV national immunisation programme for infants and older adults was introduced into the UK in 2024, RSV accounted for around 30,000 hospitalisations annually in children aged under 5 and was responsible for 20 to 30 infant deaths.[ii]

Professor Emeritus of Paediatrics at the University of Bristol, UK, Adam Finn said: “There is now very strong evidence from several countries that monoclonal antibody prophylaxis of newborn infants to prevent RSV disease in the first year of life is a highly effective way to prevent winter-time epidemics and hospital admissions. There is substantial benefit in having more than one such product available to help ensure security of supply.”

The MHRA granting of Marketing Authorisation for clesrovimab was supported by results from the pivotal Phase 2b/3 CLEVER trial (MK-1654-004), which evaluated the safety and efficacy of clesrovimab administered to preterm and full-term infants (birth to 1 year of age) entering their first RSV season,[iii] and the Phase 3 SMART trial (MK-1654-007), which evaluated the safety and efficacy of clesrovimab versus palivizumab in infants at increased risk for severe RSV disease entering their first RSV season.[iv] In both trials, clesrovimab was found to have met its primary endpoint, as well as several secondary endpoints (see Notes to Editors).iii,iv The data from these two pivotal clinical trials were recently published in the New England Journal of Medicine.

Adverse events were reported in 2,854 infants who received clesrovimab in the phase 2b/3 and phase 3 clinical studies.iii,iv The most frequent adverse reactions were injection-site pain (6.7%), injection-site erythema (4.8%), injection-site swelling (3.7%) and rash (0.5%).iii,iv Most of the adverse reactions were mild or moderate.iii,iv

Ben Lucas, Managing Director UK & Ireland at MSD said: “We’re delighted with today’s news and the fact that the UK now has another preventative option to tackle the burden of RSV on families and communities. As the NHS continues its shift from sickness to prevention, we encourage UK policymakers to continually review impact of programmes to ensure equitable access to preventable innovations from birth.”

In 2024, the UK introduced an RSV vaccination programme in both pregnant mothers and older adults.ii Infants born very or extremely prematurely (less than 32 weeks) during or preceding their first RSV season are offered a monoclonal antibody (mAb) in the UK.v To reduce the risk of severe disease, eligible high-risk infants and young children are recommended to receive RSV mAb immunisation.[v]