IMpact-RSV Study Group Report

To the Editor. The authors of the IMpact-RSV Study Group are to be commended for successfully carrying out the large multicenter trial of palivizumab.1 I wish to offer the following comments regarding the study: The authors have not stated that education regarding prevention of respiratory syncytial virus (RSV) was done similarly in the treatment and placebo groups. Simple measures like hand-washing and limiting contact with older siblings and adults can reduce RSV transmission. Despite blinding of the nature of the intervention, it is possible that these measures were unevenly distributed in the two groups and led to reduced hospitalization, thereby confounding the effects of palivizumab. The authors have not stated the sample size computation. Also, it is not clear if the analysis of results was performed on an “intention-to-treat” basis. The primary outcome of the study was a reduction in hospitalization for RSV infection from 10.6% to 4.8%. With this absolute risk reduction of 5.8% the number needed-to-treat works out to be 17 with 95% confidence limits of 11 to 36. This would mean that anywhere from 11 to 36 infants would have to be treated with monthly injections of palivizumab for 5 months to prevent one hospitalization from RSV. The average duration of hospitalization in the placebo group was 2.4 days per infant. The cost of one injection of palivizumab is approximately $1200, which means that anywhere from $66 000 to $216 000 would have to be spent to prevent one such hospitalization. This is not including the costs of the special clinics that are being set up to administer palivizumab, costs for the parents to travel to these clinics or to the pediatrician's office, the costs of missing work to keep this appointment, the expense of the parents paying for the drug themselves, and other possible expenses. In the …