Palivizumab (Synagis®, MedImmune, LLC, Gaithersburg, MD, USA) was developed by grafting the six complementarity determining regions (CDRs) of mouse MAb to human frameworks5). Palivizumab has received US FDA license in 1998, and it has been used to prevent serious lower respiratory tract infection caused by RSV infection ever since. The safety and efficacy was proven even for high-risk patients since then and currently, it is recognized as the gold standard in RSV prevention. Even in times when RSV-IVIG was being used, palivizumab was preferred because of the easy method of administration (intramuscular injection) and lower interference to MMR and varicella vaccine. Since RSV-IVIG is no longer available, palivizumab is the only licensed product for prevention of RSV infection. Infants diagnosed as CHD are considered as high-risk group for severe lower respiratory infection due to RSV infection, therefore immunoprophylaxis is recommended using palivizumab2,6,7,13-16). Patients with hemodynamically significant cyanotic and acyanotic CHD should start administration of palivizumab before the RSV season starts. Commonly recommended administration dose for palivizumab is 15 mg/kg, intramuscularly once per month for a maximum of five doses2,3). For most of the patients, the compliance under this schedule is tolerable. However, for the few non-compliant patients, home-based program for scheduled palivizumab administration may be helpful in reducing hospitalization caused by RSV infection17). Hemodynamically significant CHD is described in Table 118). In these CHD infants categorized as high-risk group for RSV infection, if RSV prevention is not conducted effectively, mortality after hospitalization is known to increase3). Particularly in these vulnerable infants who are less than 6 months old, the result of RSV infection is more catastrophic. These patients are more prone to hospitalization in the intensive care unit and they have higher possibility of ventilator care19). The blood level of palivizumab after operation under cardiopulmonary bypass may drop by 58%, therefore CHD patients who need continuous prevention for RSV needs to administer palivizumab (15 mg/kg) soon after operation2). Through a randomized controlled study the effectiveness of palivizumab for RSV infection in CHD patients has been proven4). In this study, patients who were administered palivizumab were hospitalized less often (5.3 versus 9.3%), were in need of oxygen administration less often (178 versus 658), and the total of hospitalization days were reduced (367 versus 876). Therefore, the use of palivizumab in prevention of RSV infection in CHD patients can be cost-effective in both the medical aspect of the patients as well as the socio-economic aspect20-22). Although there are many studies reporting the advantages in socio-economic aspects after prophylaxis of RSV infection in CHD patients under the age of 2 years, Korean medical insurance restricts the use of palivizumab to infants of hemodynamically significant CHD patients under the age of 1 year, unfortunately. Further studies and proposals in this matter are imminent. Complications after administration of palivizumab are very rare (<1 per 100,000 recipients), but there was a report of severe hypersensitivity18). However, in a study reporting on the safety of palivizumab, there were no significant complications reported in the 2 years that palivizumab was administered, which may prove that it is safe to use23,24). In some studies, there were reports on RSV infection resistant to palivizumab25). However, there was a report observing 458 infants who were administered with palivizumab without any mutation, which may also prove that palivizumab is effective in RSV infection prophylaxis without much complication26). Recently, the idea that palivizumab can be used not only for prophylaxis but also for treatment has been mentioned. However, further study for treatment effect of palivizumab to RSV in a large population is warranted27,28).

Motavizumab (MEDI-524, Numax®, MedImmune, LLC, Gaithersburg, MD, USA) is a second generation monoclonal antibody for RSV. It is known to be more potent than palivizumab to RSV infection in high-risk patients. Motavizumab has passed the US FDA biologic license application in January of 2008 and is under a large scale clinical study29,30).