Respiratory syncytial virus (RSV) is one of the common viruses that cause coughs and colds in the winter period. The virus is in the same family as the human parainfluenza viruses and mumps and measles viruses. In the UK RSV occurs regularly each year with epidemics generally start in November or December and lasting for four to five months, peaking over the Christmas and New Year period. The very young (less than 1 year of age) and the elderly are at the greatest risk of developing severe illness from RSV infection. Risk factors that increase the risk of acquiring RSV include birth within 6 months of an RSV season. Children born prematurely, or with underlying chronic lung disease are also at increased risk of developing severe disease. Palivizumab (Synagis™, Abbott Laboratories Limited) is a recombinantly produced monoclonal antibody directed against the surface RSV fusion protein (F-protein), which is essential for RSV to enter the host target cell. The Joint Committee on Vaccination and Immunisation (JCVI) has advised that prophylaxis with palivizumab is recommended in certain groups of infants: 1. Children under 2 years of age with chronic lung disease, on home oxygen or who have had prolonged use of oxygen. 2. Infants less than 6 months of age who have left to right shunt haemodynamically significant congenital heart disease and/or pulmonary hypertension. 3. Children under 2 years of age with severe congenital immunodeficiency. Currently there are 2 randomised controlled trials (RCTs) available which appear to be the only published clinical trial evidence to support the JCVI recommendations 1 and 2. However recommendation 3 does not seem to be based on published or unpublished RCT data. The first trial investigated the use of palivizumab prophylaxis in high risk children and the second investigated its use in infants and children with haemodynamically significant congenital heart disease. Although both trials found palivizumab to significantly reduce the incidence of hospitalisation (primary endpoint), there was no significant difference in the secondary endpoint measures of ICU admissions and mechanical ventilation between the placebo and palivizumab groups in both trials. Both trials have raised numerous concerns, covered in the review. The majority of adverse drug reactions seen in the clinical trials were transient and mild to moderate in severity. Common (> 1/100) adverse drug reactions for palivizumab include fever, injection site reactions and nervousness. Furthermore, there have not been any specific studies investigating the cost-effectiveness of palivizumab therapy. The JCVI estimated that palivizumab prophylaxis would be suitable in 0.3% of live births, however, research from North West London suggests that this figure could be as high as 1.1% of live births. If this is the case, then palivizumab could have cost implications of up to approximately £67 million in England and Wales or £130,000 per 100,000 population. This is the drug cost only.