Immunizing infants in the U.S. against pneumonia led to fewer hospitalizations for the infection during the past decade, with the largest effect on the youngest and oldest, according to a nationwide study.
The study, which appears in the July 11 issue of the New England Journal of Medicine, showed a 10.5% decrease in overall pneumonia hospitalizations for all ages after the 7-valent pneumococcal conjugate vaccine was added to the U.S. infant immunization schedule in 2000.
The decline represents 168,000 fewer hospitalizations than would have been predicted for 2009 based on data from 1997-99, before the PCV7 was added, according to lead author Marie Griffin, MD, MPH, professor of preventive medicine at Vanderbilt University in Nashville, Tenn., and colleagues.
“Pneumonia is a leading cause of hospitalization in the United States,” Griffin said in the release. “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.”
The group looked at data from the Agency for Healthcare Research and Qualitys National Inpatient Sample on the number of pneumonia-related hospitalizations from 1997-2009. They found 17,892,085 hospitalizations for pneumonia, representing 4.1% of all U.S. hospitalizations other than those for childbirth.
The researchers found a 43.2% reduction in hospitalizations of children ages 2 and younger. Most of the reduction occurred shortly after the introduction of the vaccine. For older children and adults, who did not receive PCV7, the study showed a small decline in cases that gradually became a larger decline during the 10 years after the vaccines introduction.
By 2009, more than half the nationwide decline in pneumonia hospitalizations could be attributed to older adults, with 73,000 fewer annual hospitalizations — a 22.8% decrease — for those ages 85 and older, according to the study. That population has an in-hospital mortality rate ranging from 7% to 12%, they wrote in the study discussion.
The PCV7 was designed to prevent blood and ear infections in children caused by seven common types of the pneumococcal bacteria, according to the news release, but questions remained about whether another type would reduce gains made by the vaccine. Even with increases in pneumonia caused by nonvaccine serotypes, the overall rate of hospitalizations decreased, the study found.
According to co-author Carlos Grijalva, MD, MPH, assistant professor of preventive medicine at Vanderbilt, pneumococcal bacteria can live in the noses and throats of healthy people, especially children, and then be transmitted to older age groups. By 2009, the carriage of serotypes included in the PCV7 was significantly reduced, the authors wrote.
Study abstract: www.nejm.org/doi/full/10.1056/NEJMoa1209165#t=abstract.