Revised Indications for the Use of Palivizumab and Respiratory Syncytial Virus Immune Globulin Intravenous for the Prevention of Respiratory Syncytial Virus Infections

BACKGROUND

RSV-IGIV (RespiGam, Massachusetts Public Health Biological Laboratories and MedImmune Inc, Gaithersburg, MD) was licensed by the Food and Drug Administration in January 1996 for prevention of severe RSV lower respiratory tract disease in infants and children younger than 24 months with CLD or a history of preterm birth (≤35 weeks’ gestation). Two randomized, controlled clinical trials demonstrated that monthly RSV-IGIV infusions in high-risk infants resulted in a 41% to 63% decrease in the rate of hospitalization attributable to RSV infection of the lower respiratory tract.^1,2 Although this was the first agent with demonstrated efficacy for prophylaxis against RSV infections of the lower respiratory tract, several disadvantages are associated with this product. RSV-IGIV is contraindicated for use in children with hemodynamically significant heart disease, particularly cyanotic heart disease, because of safety concerns detailed later in this report. Further, RSV-IGIV prophylaxis requires intravenous access with a 4-hour infusion each month during the RSV season and infrequently presents problems with volume overload. Immune Globulin Intravenous is known to interfere with the immune response to some live-virus vaccines. Although no issues of contamination with adventitious agents have been encountered, this is a theoretic concern. Finally, shortages of RSV-IGIV occurred during 2 RSV seasons.

In June 1998, the Food and Drug Administration licensed palivizumab (Synagis, MedImmune, Gaithersburg, MD) for administration as a monthly intramuscular injection for the prevention of serious respiratory disease caused by RSV in infants and children with a history of preterm birth (≤35 weeks’ gestation) or CLD. Approval was based on results of a randomized, placebo-controlled trial (IMpact-RSV trial) that demonstrated a 55% decrease in the rate of hospitalization among children with a history of preterm birth and/or CLD.³ A second trial with palivizumab has been completed in infants and children with hemodynamically significant CHD that demonstrated safety and a 45% decrease in the rate of RSV-associated hospitalization compared with placebo recipients.⁴ Because palivizumab is not derived from Human Immune Globulin, it is free of potential contamination by infectious agents. It can be produced readily in batch lots, and therefore shortages are not anticipated. Palivizumab will not interfere with the immune response to any vaccine in the immunization schedule. Thus, palivizumab has become the agent of choice for monthly prophylaxis in most high-risk infants. Recommendations for the use of both products have been summarized by the American Academy of Pediatrics.^5,6 The purpose of this report is to update clinicians on the appropriate use of RSV-IGIV and palivizumab on the basis of data from 5 clinical trials.

CLINICAL STUDIES WITH RSV-IGIV

Results of the first multicenter randomized controlled trial with prophylactic RSV-IGIV in infants younger than 48 months at enrollment with underlying BPD, CHD, or a history of preterm birth (≤35 weeks’ gestation) are shown in Table 1.¹ Eighty-one infants received RSV-IGIV at a dosage of 750 mg/kg per infusion, 79 infants received 150 mg/kg, and 89 infants received no infusions. Participants in the intervention arms received monthly RSV-IGIV infusions from mid-November through March or April; at least 75% of the dose was infused at 85% of the visits. Infants receiving RSV-IGIV at a dosage of 750 mg/kg had significantly decreased RSV-associated lower respiratory tract disease severity, frequency of hospital admissions, and number of days in the hospital or intensive care unit (ICU). Monthly RSV-IGIV infusions were well tolerated. Serum RSV-neutralizing antibody titers in infants receiving RSV-IGIV at a dosage of 750 mg/kg usually exceeded 1:200, a titer close to the threshold required for protection in animals. Adverse reactions occurred in 3% of 580 infusions and consisted of mild decreases in oxygen saturation, fever, and mild fluid overload. Six deaths occurred (3 in the high-dose group and 3 in the low-dose group); none of the deaths were considered related to infusion of RSV-IGIV or to RSV infection, and 3 of the deaths were related to complications of cardiac surgery. Monthly RSV-IGIV infusions during the respiratory season resulted in a 63% and 82% decrease in the rate of RSV-associated hospitalization and disease severity, respectively. Patients benefiting most were preterm infants and infants with BPD.

Results from a second multicenter randomized albumin placebo-controlled trial (PREVENT study²) in 510 infants younger than 24 months with BPD and/or history of preterm birth are shown in Table 2. Monthly RSV-IGIV infusions decreased the RSV-associated illness frequency and severity by 41% to 60%. The decrease in the rate of RSV-associated hospitalization was greater for infants and children with BPD than for those with history of preterm birth only (49% vs 20%, respectively; Table 2). Moderate to severe adverse events consisting of fever, increased respiratory distress, and rash were no more frequent in patients receiving RSV-IGIV than in control patients. These adverse events were easily managed medically and did not occur with subsequent infusions. Of additional interest, children receiving RSV-IGIV had a 50% decrease in the rate of hospitalization for respiratory illness of any cause. In addition, recipients of high-dose RSV-IGIV experienced significantly fewer episodes of acute otitis media than did children in the control group.⁷

RSV-IGIV USE IN PATIENTS WITH CHD

Two trials with RSV-IGIV included infants and children with CHD.^1,8 As part of the initial National Institutes of Health-sponsored RSV-IGIV trial, 87 infants with CHD were enrolled among 249 high-risk subjects. Results of this trial demonstrated an overall 63% decrease in the rate of RSV-associated hospitalization compared with the control group, but the trial was not powered for subgroup analysis, and thus the results for children with cardiac disease were not analyzed separately.¹ A second trial conducted in 1994–1995 evaluated 416 children younger than 48 months with CHD who were assigned to a group receiving monthly RSV-IGIV or a control group.⁸ Results showed a trend in RSV disease prevention that did not reach statistical significance. Interpretation of results in the second study was confounded by an unexplained difference in randomization between treatment and control groups, resulting in a significantly higher proportion of children with cyanotic CHD in the treatment group than in the control group. In both trials, an unexpected increase in surgically related adverse events, including mortality, in RSV-IGIV recipients occurred. Although the precise explanation for the increase in mortality in infants with cyanotic heart disease is unclear, it may have been caused by an alteration in blood viscosity after administration of RSV-IGIV to patients with an elevated hematocrit concentration. As a consequence of the concerns raised by these studies, RSV-IGIV is contraindicated for use in infants with severe CHD.

CLINICAL STUDIES OF EFFICACY OF PALIVIZUMAB

CARDIAC TRIAL

A randomized, double-blind, placebo-controlled trial with palivizumab was conducted between 1998 and 2002 involving 1287 infants and children with hemodynamically significant CHD.⁴ Subjects were randomized 1:1 to receive 5 monthly intramuscular injections of palivizumab (15 mg/kg) or placebo and stratified at entry by cardiac lesion to a cyanotic or noncyanotic group. Palivizumab recipients had a 45% decrease in the rate of RSV-related hospitalization (9.7% in the placebo group vs 5.3% in the palivizumab group [P = .003]). There was a 56% decrease in total days of RSV-associated hospitalization per 100 children (P = .003) and a 73% decrease in total RSV-associated hospital days with supplemental oxygen per 100 children (P = .014). Serious adverse events occurred in 63.1% of placebo recipients and 55.4% of palivizumab recipients (P < .005). No serious adverse events were related to palivizumab. There was not a significant difference in deaths between groups (3.7% in placebo recipients vs 3.3% in palivizumab recipients). No deaths were attributed to the study drug. After cardiac bypass surgery, the mean serum palivizumab concentration was decreased by 58%. The results of this study demonstrated safety and efficacy of monthly palivizumab immunoprophylaxis in infants and children with hemodynamically significant CHD.

OVERALL CONSIDERATIONS

A critical aspect of RSV prevention in high-risk infants is the education of parents and other caregivers about the importance of decreasing infants’ exposure to and acquisition of RSV. Preventive measures include eliminating exposure to cigarette smoke and settings where RSV or other respiratory viruses may be transmitted (eg, child care centers). Emphasis on hand hygiene also is important in all settings including the home, especially during periods when contacts of high-risk children have respiratory tract infections or when infants are at risk of exposure to respiratory infections from siblings who are in child care or who attend school.

Both palivizumab and RSV-IGIV have been shown to decrease the risk of severe RSV disease in high-risk infants and children. No direct studies have been conducted to compare the relative efficacy of the 2 interventions. Because of its ease of administration, monthly palivizumab generally is favored over RSV-IGIV (an intramuscular injection vs a 4-hour intravenous infusion).

Limited data are available regarding the use of palivizumab for 2 consecutive seasons. No difference was noted between incidence of adverse events among children who received palivizumab prophylaxis for a second season and children receiving prophylaxis for only 1 season.¹¹ In addition, limited experience from postmarketing data suggest that adverse events occurring after more than 5 doses in a single season are no different from adverse events occurring after the initial 5 doses.¹¹

Postmarketing surveys indicate that the effect of palivizumab prophylaxis on the rate of hospitalization for RSV is similar to that found in controlled clinical trials.^12,13 Rare cases of severe hypersensitivity reactions (<1 case per 100 000 recipients) have been described after an initial dose as well as after reexposure to palivizumab.¹¹

Palivizumab attaches to a well-conserved epitope in the A-antigenic site of the F protein of RSV.⁹ Although resistant RSV strains can be generated in laboratory experiments, naturally occurring escape mutants (ie, resistant viruses) to palivizumab have not been identified after the administration of this product. Ongoing surveillance of RSV isolates has failed to identify any decrease in sensitivity to palivizumab.

COST-BENEFIT ANALYSES

Several economic analyses of RSV immunoprophylaxis have been published^14–20 and reviewed.²¹ The primary benefit of immunoprophylaxis with either agent is a decrease in the rate of RSV-associated hospitalization. None of the 5 randomized, controlled clinical trials have demonstrated a significant decrease in rate of mortality attributable to RSV infection in infants who receive prophylaxis. Most of the economic analyses fail to demonstrate overall savings in health care dollars because of the high cost if all at-risk children were to receive prophylaxis. Estimates of cost per hospitalization prevented have been inconsistent because of considerable variation in the baseline rate of hospitalization attributable to RSV in different high-risk groups. Other considerations that will influence results include the effect of prophylaxis on outpatient costs and a resolution of the question of whether prevention of RSV infection in infancy decreases wheezing and lower respiratory tract problems later in childhood.

Factors other than degree of prematurity, CHD, and CLD that may influence the decision regarding prophylaxis include presence of other underlying conditions that predispose to respiratory complications (eg, neurologic disease in very low birth weight infants), number of young siblings, child care center attendance, anticipation of cardiac surgery, and distance to and availability of hospital care for severe respiratory illness. For many infants who qualify for the approved indications, risk of hospitalization for serious respiratory illness will be low, and the cost and logistic difficulties associated with prophylaxis may outweigh potential benefits.

INDICATIONS FOR RSV PROPHYLAXIS

Detailed recommendations for RSV prophylaxis are available in the accompanying policy statement.²²

Committee on Infectious Diseases, 2002–2003

Jon S. Abramson, MD, Chairperson

Carol J. Baker, MD

Robert S. Baltimore, MD

Joseph A. Bocchini Jr, MD

Sarah S. Long, MD

Julia A. McMillan, MD

H. Cody Meissner, MD

Keith R. Powell, MD

Charles G. Prober, MD

Margaret B. Rennels, MD

Thomas N. Saari, MD

Leonard B. Weiner, MD

Liaisons

Joanne Embree, MD

Canadian Paediatric Society

Marc A. Fischer, MD

Centers for Disease Control and Prevention

Bruce G. Gellin, MD, MPH

National Vaccine Program Office

Caroline B. Hall, MD

Section on Infectious Disease

Martin C. Mahoney, MD

American Academy of Family Physicians

Mamodikoe Makhene, MD

National Institutes of Health

Walter A. Orenstein, MD

Centers for Disease Control and Prevention

Douglas R. Pratt, MD

Food and Drug Administration

Jeffrey R. Starke, MD

American Thoracic Society

Jack Swanson, MD

American Academy of Pediatrics Practice Action Group

Ex Officio

Larry K. Pickering, MD

Red Book Editor

Consultant

Edgar O. Ledbetter, MD

Staff

Martha Cook, MS

Commitee on Fetus and Newborn, 2003–2004

Lillian Blackmon, MD, Chairperson

Daniel G. Batton, MD

Edward F. Bell, MD

Susan E. Denson, MD

William A. Engle, MD

William P. Kanto, Jr, MD

Gilbert I. Martin, MD

Ann R. Stark, MD

Liaisons

Keith J. Barrington, MD

Canadian Paediatric Society

Tonse Raju, MD, DCH

National Institutes of Health

Laura E. Riley, MD

American College of Obstetricians and Gynecologists

Kay M. Tomashek, MD

Centers for Disease Control and Prevention

Carol Wallman, MSN, RNC, NNP

National Association of Neonatal Nurses

Saff

Jim Couto, MA