AstraZeneca's MedImmune is partnering with Sanofi's vaccines arm Sanofi Pasteur on the development and commercialisation of its experimental monoclonal antibody MEDI8897 for the prevention of Respiratory Syncytial Virus (RSV) associated illness in newborns and infants.

MEDI8897 neutralised RSV by binding the RSV fusion (F) protein expressed on virions and infected cells; it has been engineered to have a long half-life so that only one dose would be needed for the entire RSV season.

The drug is being developed for the passive immunisation of infants, and is currently being investigated in a Phase IIb study in preterm infants with plans for a Phase III trial in healthy full-term infants.

Under the terms of the deal, Sanofi Pasteur will make an upfront payment of 120 million euros and also up to 495 million euros upon achievement of certain development and sales-related milestones. Both parties will share all costs and profits equally.

MedImmune will continue to lead all development activity up to the first approval, and AstraZeneca will retain MEDI8897 manufacturing activities, and Sanofi-Pasteur will lead the commercialisation activities for the drug.

RSV is the most common cause of lower respiratory tract infections in children younger than one year of age in the US and worldwide.

"RSV is considered to be the most important missing indication in the vaccination schedule of newborns," said David Loew, Sanofi Executive Vice President and head of Sanofi Pasteur. "As a global leader in the paediatric vaccine industry, this deal with MedImmune therefore makes perfect sense for Sanofi Pasteur."

MEDI8897 received fast-track designation from the US Food and Drug Administration in 2015.