Immunization of infants with pneumococcal conjugate vaccine has wide preventive effects
The introduction of a seven-valent pneumococcal conjugate vaccine (PCV7), a vaccine against seven serotypes of the bacterium S. pneumoniae, has had dramatic effects on a variety of diseases caused by this bacterium, according to a new literature review by researchers at Vanderbilt University School of Medicine. S. pneumoniae is a frequent cause of dangerous blood infections, meningitis, pneumonia, and otitis media worldwide.
Administration of PCV7 to young children began in the United States in the year 2000, after the vaccine was licensed by the Food and Drug Administration (FDA). The uptake of the vaccine was fast and by the end of 2005, approximately 87 percent of U.S. children between aged 19 to 35 months had received three or more doses of PCV7.
From 1998 to 2003, rates of invasive pneumococcal diseases in children less than 5 years old declined 75 percent. Furthermore, a 42 percent reduction in rates of invasive disease among infants under 2 months old (too young to be immunized), suggested indirect protection or "herd immunity" derived from immunization of older children. Similar declines in rates of invasive pneumococcal disease have been consistently observed in older age groups for whom PCV7 was not recommended. Most serotypes covered by PCV7 were antibiotic resistant and after introduction of PCV7, there was a substantial decline in invasive disease due to nonsusceptible pneumococcal strains. In addition, declines in rates of hospitalizations for pneumonia among children under 2 years of age (the target population of the immunization program) also declined. By the end of 2004, rates of all-cause pneumonia hospitalizations among children less 2 years old had declined by 39 percent from what would be expected based on pre-PCV7 trends. Moreover, rates of pneumonia hospitalizations declined significantly among young adults aged 18 to 39 years, suggesting indirect protection given that this age group includes parents of vaccinated young children.
Although invasive disease caused by serotypes included in PCV7 declined substantially, there was an increase in disease caused by serotypes not covered in the vaccine. However, in the general population of the United States, this increase has only modestly eroded the gains made by the vaccine. Some nonvaccine serotypes have become important pathogens and monitoring of the changes in the epidemiology of pneumococcal diseases is necessary. New pneumococcal conjugate vaccines with wider coverage are in development and are expected to further reduce the burden of pneumococcal diseases.
The study was funded in part by the Agency for Healthcare Research and Quality (HS16784). More details are in "Population-based impact of routine infant immunization with pneumococcal conjugate vaccine in the USA," by Carlos G. Grijalva, M.D., M.P.H., and Marie R. Griffin, M.D., M.P.H., in Expert Review of Vaccines 7(1), pp. 83-95, 2008.
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