Vaccine Has Led to Changes in Pneumococcal Infections

In the decade since the introduction of pneumococcal vaccination, significant shifts have occurred in the bacterial strains causing serious pneumococcal infections in children, according to a pair of studies in the April issue of the Pediatric Infectious Disease Journal.

The two studies—one from Massachusetts and one from Texas—find that the most common cause of invasive pneumococcal infections is now a strain called serotype 19A, which is not prevented by the current pneumococcal vaccine. The studies also document a rising rate of infections caused by antibiotic-resistant pneumococci.

In Massachusetts, Serotype 19A Is Now Most Common Cause of Infection

A study led by Dr. Katherine K. Hsu of Boston University used a microbiology database to analyze trends in pneumococcal infection among Massachusetts children since introduction of the "PCV7" pneumococcal vaccine in 2000. Before PCV7 vaccination, pneumococci were the leading cause of invasive bacterial infections in children, including pneumonia, meningitis and bloodstream infection.

Pneumococcal vaccination is currently recommended for all children before age two. The vaccine is called PC7 because it protects against seven major disease-causing strains of pneumococci.

From 2001 to 2007, only 15 percent of serious pneumococcal infections in Massachusetts were caused by one of the seven strains covered by the PC7 vaccine. The remaining 85 percent were caused by other strains, most commonly serotype 19A.

As infections with PC7-covered strains decreased, infections with strains not covered by PC7 increased—as a result, the overall rate of serious infections remained about the same. Although most of the children recovered from their infection, the fatality rate was 1.4 percent. Most of the deaths occurred in infants less than one year old.

Texas Study Shows Increase in Antibiotic-Resistant Pneumococci

A study led by Dr. Chonnamet Techasaensrir of University of Texas Southwestern Medical Center, Dallas, found that invasive pneumococcal infections decreased after the introduction of PCV7. However, from 2006 to 2008, the infection rate began to rise again. As in Massachusetts, more infections were caused by serotype 19A.

There was also a significant increase in infections caused by antibiotic-resistant pneumococci—mainly serotype 19A. This is of special concern because these antibiotic-resistant bacteria were not previously identified in Dallas; the Massachusetts study also showed an increased rate of antibiotic resistance. Both groups of researchers highlight the need for continued surveillance to monitor trends in invasive pneumococcal infections and the emergence of antibiotic-resistant strains.

The new results are consistent with worldwide data on trends in pneumococcal infection, according to an accompanying editorial by Dr. Steve Black of Cincinnati Children's Hospital. He stresses that the fluctuations in infection rates and the emergence of antibiotic-resistant bacteria do not mean that the PCV7 vaccination program is a failure—patterns of antibiotic use have probably played a more important role in the shift toward serotype 19A. "It must be emphasized that introduction of PCV7 in the United States has resulted in an overall reduction in invasive pneumococcal disease in children of almost 80 percent," Black writes.