Motavizumab (MEDI-524, NUMAX, NISTmAb) is a second generation monoclonal antibody (mAb) derived from palivizumab (Synagis) using affinity maturation techniques. Motavizumab is currently undergoing US Food and Drug Administration review as a treatment for respiratory syncytial virus (RSV) prophylaxis. It has been evaluated in large-scale clinical studies, and has demonstrated efficacy in reducing the disease burden of RSV in high-risk infant populations. Motavizumab (MEDI-524, NUMAX, NISTmAb) has higher affinity and a longer half-life, was effective in reducing RSV hospitalization in high-risk full-term infants in the US, but was not licensed due to safety concerns (allergic reactions).