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Researchers from Vanderbilt University found childhood vaccinations against pneumococcal bacteria have reduced pneumonia hospitalizations by 10 percent, particularly among older adults. They noted that this so-called "herd immunity" is more effective than the vaccine that is recommended for adults to prevent the spread of pneumonia.
"Pneumonia is a leading cause of hospitalization in the United States. The protective effect we saw in older adults, who do not receive the vaccine but benefit from vaccination of infants, is quite remarkable. It is one of the most dramatic examples of indirect protection or herd immunity we have seen in recent years," study author Dr. Marie Griffin, a professor of preventive medicine and medicine at Vanderbilt, said in a university news release.
In conducting the study, the researchers analyzed a large national database to identify hospitalizations due to pneumonia from 1997 to 2009. Their aim was to determine how the pneumococcal conjugate vaccine (PCV7 or Prevnar) affected rates of pneumonia since it was introduced in 2000.
The study, published in the July 11 issue of the New England Journal of Medicine, found that since the vaccine was introduced there has been a 40 percent drop in pneumonia hospitalizations among children younger than 2. Although there was also a decline in hospitalizations among older children and adults who did not receive the vaccine, the researchers pointed out that by 2009 more than half the nationwide decline in pneumonia hospitalizations involved adults older than 65. In fact, hospitalizations among adults aged 85 or older fell by about 70,000 annually.
"This group of bacteria can live in the nose and throat of healthy people, especially children. From young children, these bacteria may be transmitted to older age groups. Over time, the vaccine is causing a change in types of pneumococcus carried and transmitted nationwide. We are very fortunate to witness this in our time. These huge indirect effects on the adult population don't happen very often," study co-author Dr. Carlos Grijalva, an assistant professor of preventive medicine at Vanderbilt, said in the news release.
PCV7 was initially developed to protect children against lung and ear infections as well as potentially fatal blood and spinal infections caused by seven types of pneumococcal bacteria. After it was introduced, however, questions remained about whether the effects of the vaccine would last or if other less common types of pneumococcal bacteria would increase.
"Sometimes when you eliminate one serotype, others become more apparent. Following the introduction of PCV7, there was an increase in pneumococcal diseases caused by a serotype called 19A, not included in that vaccine. That's why it is really important to keep studying this and seeing what happens," Griffin explained.
The latest version of the pneumococcal vaccine, introduced in 2010, includes 19A. Known as PCV13, the vaccine protects against 13 types of pneumococcus.
"PCV13 may cause another large reduction in pneumonia hospitalizations; perhaps another 10 percent, we hope," Griffin said. "It is important for people to know that adults are benefiting from our childhood vaccine program. These are adults who won't be hospitalized, won't be getting antibiotics, or complications of hospitalizations, and won't be dying, since the risk of death is 5 percent to 12 percent when older adults are hospitalized with pneumonia."
The U.S. Centers for Disease Control and Prevention funded the study.
-- Mary Elizabeth Dallas
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