Sanofi and AstraZeneca have reported positive top-line data from the Phase II/III MEDLEY clinical trial of nirsevimab in infants at high risk of respiratory syncytial virus (RSV) infection.

The trial enrolled a total of 925 preterm infants or those suffering from chronic lung disease (CLD) or congenital heart disease (CHD) entering their first RSV season.

It evaluated the safety and tolerability of the drug, determined as treatment-emergent adverse events and treatment-emergent serious adverse events over 360 days after dosing.

Data showed that nirsevimab’s safety and tolerability profile was favourable and similar to that of Synagis (palivizumab).

The randomised, double-blind, palivizumab-controlled study is continuing to gather more safety data in infants with CLD or CHD who receive dosing before the second season.

RSV is a contagious, seasonal virus that affects the respiratory tract. It is a common cause of hospitalisations in infants worldwide.

Nirsevimab is an experimental, extended half-life RSV monoclonal antibody designed to provide passive immunisation for preventing lower respiratory tract infections (LRTI) caused by the virus.

The drug is intended for use from birth in infants born in the RSV season, or at the season’s beginning for infants entering their first RSV season. It can also be given to infants with CLD or CHD entering their first and second RSV season.

Sanofi and AstraZeneca partnered in March 2017 to develop and commercialise nirsevimab.

Sanofi Pasteur Research and Development global head Jean-François Toussaint said: “RSV is the major remaining paediatric infectious disease with no preventative option available to all infants.

“We believe nirsevimab has the potential to become an important and innovative routine immunisation for all infants, those born prematurely or at term, healthy or with health conditions.”

In April this year, nirsevimab was reported to have met the primary endpoint of the Phase III MELODY trial with a statistically significant decrease in RSV-related LRTI in healthy preterm and term infants.

Along with the Phase IIb trial data, MELODY and MEDLEY results contribute to the evidence showing the drug’s potential to protect all infants against RSV with a single dose.

This combined data will be included in regulatory submissions planned for next year.