Respiratory syncytial virus - motavizumab

Respiratory syncytial virus is a common viral infection in infants, with almost all children being infected in their first two years. Premature babies are particularly at risk, as are those with underlying heart and lung conditions. There is no broad spectrum antiviral agent that successfully treats the virus, and thus passive immunoprophylaxis is the only way to reduce hospitalisation rates.

One such antibody, Synagis (palivizumab), is already available but it does not provide complete protection or inhibit the virus from replicating in the upper respiratory tract.

AstraZeneca (MedImmune) is developing motavizumab as an alternative.¹ The affinity enhanced humanised monoclonal antibody is designed to improve on palivixumab's ability to bind to the virus. In a dose escalation study, 211 children were given 15mg/kg of the antibody in the first RSV season, and in the second season 136 were randomised to receive either motavizumab or palivizumab.² The most commonly reported adverse event was transient erythema at the injection site. No increase in adverse reactions or immunogenicity was seen during or after the second season, which supported further development of the antibody.

Phase III trials have now been carried out. In one, 6,635 preterm infants were given motavizumab or palivizumab; 26% fewer of those treated with the new antibody were hospitalised as a result of RSV infection, and 50% fewer outpatient lower respiratory infections. In another study, 1,410 full term infants under six months were given motavizumab or placebo. Hospitalisations were 83% lower in the antibody group, and outpatient treatment for RSV infection 71% lower. Trials continue.