Vaccines In Development
Respiratory Syncytial Virus
Respiratory syncytial virus (RSV) is the most common cause of bronchiolitis—inflammation of the bronchioles (small airways) which causes wheezing—as well as pneumonia among infants and children under 1 year of age. (1) It is estimated that by 2 years of age almost all children will have been infected with RSV, and half of them will be infected twice. (2) Re-infection throughout life—usually upper respiratory infection—is common.
Most healthy infants infected with RSV are not hospitalized. However, infants with underlying lung or heart disease and those with immune deficiency are at increased risk of severe or fatal RSV infection. Each year in the United States, it is estimated that between 70,000 and 126,000 infants are hospitalized with RSV pneumonia or bronchiolitis. (3)
In some children, RSV bronchiolitis early in life has been associated with reactive airway disease (asthma) later in life. This association is poorly understood and may merely reflect the child’s underlying predisposition to reactive airway disease.
RSV infection increases the risk for developing superinfection with bacteria, resulting in ear infection, sinusitis or pneumonia.
The elderly are also at risk of severe RSV disease, with 14,000 to 62,000 hospitalizations occurring annually in the US. (4)
There are two subtypes of RSV virus—group A RSV and group B RSV—that circulate concurrently each year during the winter and early spring.
The virus is spread through contaminated nasal secretions, usually transmitted by close contact with an infected person or by touching contaminated surfaces. Transmission control is especially important in health care settings because many patients with underlying risk factors are frequent users of health care. (5)
Treatment of RSV infections is supportive care. Antimicrobial agents are rarely indicated. Corticosteroids are not effective. (6)
There is no currently licensed vaccine against RSV. However, one product is available to prevent RSV infections in selected children under 2 years of age:
Palivizumab is administered every 28-30 days, beginning just before the RSV season until completing a total of 5 doses.
In the US, the first dose of palivizumab should be administered at the beginning of November, and the last dose should be administered at the beginning of March, which will provide protection into April. The epidemiology of RSV in communities can also be considered in the decision to begin and end palivizumab administration.
Palivizumab is only recommended for the short term prevention—not treatment—of RSV disease in certain high-risk groups:
Palivizumab may be administered at the same time of recommended childhood vaccines. (6)
Palivizumab has been shown to be both safe and effective in reducing RSV hospitalizations in premature infants and in infants with complex heart diseases. Because of its high cost (over a thousand dollars per dose for most infants), palivizumab the cost effectiveness limits its use to high risk population. (8, 9).
There is no licensed RSV vaccine.
In the 1960s, scientists tested a formalin-inactivated RSV vaccine in infants and children. However, the vaccine did not protect against infection and was associated with an increased risk of severe RSV disease when some of the vaccinated children became infected. (2)
A successful RSV vaccine should protect against bronchiolitis and pneumonia. It is unlikely that a RSV vaccine would protect against RSV infection because natural infection does not. Developing such a vaccine has been hampered by an incomplete understanding of which immune responses provide protection against serious RSV disease.
However, using molecular technology, two types of candidate RSV vaccines are being evaluated in humans: live attenuated vaccines and sub-unit vaccines. An RSV immunization program may need to include different vaccines for the different target groups such as infants in the first year of life, expectant mothers (so the mother will pass immunity to her baby), and those who are at high risk for severe RSV disease. (2, 10, 11)
1. CDC National Center for Infectious Diseases (2004). Respiratory Syncytial Virus.
2. Karron RA (2004). Respiratory Syncytial Virus Vaccine. In: Plotkin SA, Orenstein WA (Eds). Vaccines (4th Edition, pp. 1317-1326). Philadelphia, PA: W.B. Saunders Company, 2004.
3. Shay DK, Holman RC, Newman RD et al (1999). Bronchiolitis-Associated Hospitalizations Among US Children, 1980-1996. JAMA, 282:1440-1446.
4. Han LL, Alexander JP, and Anderson LJ (1999). Respiratory Syncytial Virus Pneumonia among the Elderly: an Assessment of Disease Burden. Journal of Infectious Diseases, 179:25-30.
Falsey AR, Hennessey PA, Formica MA, et al (2005). Respiratory Syncytial Virus Infection in Elderly and High-Risk Adults. New England Journal of Medicine 352(17):1749-1759.
5. Thompson WW, Shay DK, Weintraub E, et al. (2003) Mortality associated with influenza and respiratory syncytial virus in the United States. JAMA 289:179-186.
6. AAP, Committee on Infectious Diseases (2003). Respiratory Syncytial Virus In LK Pickering (Ed.), Red Book: Report of the Committee on Infectious Diseases (26th ed., pp. 523-528). Elk Grove Village, IL: Author.
7. Committee on Infectious Diseases and Committee on Fetus and Newborn (2003). Revised Indications for the Use of Palivizumab and Respiratory Syncytial Virus Immune Globulin Intravenous for the Prevention of Respiratory Syncytial Virus Infections. Pediatrics, 112(6):1442-1446.
8. The IMpact-RSV Study Group (1998). Palivizumab, a Humanized Respiratory Syncytial Virus Monoclonal Antibody, Reduces Hospitalization From Respiratory Syncytial Virus Infection in High-risk Infants. Pediatrics, 102(3):531-537.
9. Kamal-Bahl S, Doshi J, and Campbell J (2002). Economic Analyses of Respiratory Syncytial Virus Immunoprophylaxis in High-Risk Infants: A Systematic Review. Archives of Pediatrics and Adolescent Medicine, 156:1034-1041.
11. Greenberg HB, and Piedra PA (2004). Immunization against viral respiratory disease: a review. Pediatric Infectious Disease Journal, 23(11):S254-S261.
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