- The Washington Times - Thursday, April 13, 2006

Infants too young to receive a vaccination against pneumonia, meningitis and other potentially deadly bacterial infections have experienced a drop in the rate of those diseases, possibly as a result of older children having been immunized.

The information is contained in a report by Vanderbilt University researchers, published in the current issue of Journal of the American Medical Association.

The study found a 42 percent decline in rates of invasive pneumococcal disease (IPD) caused by the bacteria, streptococcus pneumoniae, among children under 2 months old since a vaccine went on the market in February 2000.

Researchers say similar decreases in rates of IPD have been reported for children older than 5 years and adults who are not specific targets of recommendations for immunization with the so-called heptavalent pneumococcal conjugate vaccine, or PCV7. In the United States, PCV7 is recommended for all children between the ages of 2 months and 23 months. Younger babies and older youngsters are not receiving it.

Dr. Katherine A. Poehling and colleagues at the Vanderbilt University School of Medicine in Nashville, Tenn., said their report is the first to indicate that “neonates (infants up to 30 days old) and other infants too young to receive PCV7 are benefiting from herd immunity.” Herd immunity, they said, “occurs when vaccinated persons in a population indirectly protect unvaccinated ones by impeding the spread of an infectious agent.”

The authors point out that since the introduction of the childhood vaccine, Prevnar, six years ago, the IDP rate among U S. children younger than two years has decreased by at least 60 percent.

The research involved analysis of IPD data for infants from birth to 90 days old.

Researchers examined cases of bloodstream infections, meningitis, pneumonia and other examples of invasive pneumococcal diseases that afflicted babies in the study population between July 1, 1997, and June 30, 2004. Their intent was to compare rates of IPD before and after the introduction of the vaccine.

The researchers identified 146 IPD cases during the study period. They said 89 occurred before PCV7 became available, and 57 in the three years after the vaccine went on the market.

Among all infants examined in the first three months of life, the IPD rate fell significantly — from 11.8 per 100,000 live births in the pre-vaccine period to 7.2 per 100,000 live births after the vaccine arrived on the scene.

The average rate of IDP fell 39 percent between the pre- and post-vaccine periods for neonates and declined 45 percent and 32 percent, respectively, for infants 31 to 60 days old and those 61 to 90 days old.

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