Increase in Serious Pneumococcal Infections Not Covered by Childhood Pneumococcal Vaccine

Alaska Native children are experiencing increased rates of serious infections caused by strains of pneumococcal bacteria that are not covered by the current childhood pneumococcal vaccine, indicating the importance of ongoing surveillance of vaccine effectiveness, according to a study in the April 25 issue of JAMA.

Before introduction of 7-valent pneumococcal conjugate vaccine (PCV7), Alaska Native children and adults experienced high rates of invasive pneumococcal disease (IPD) compared with non-Native Alaskans. Introduction of PCV7 into the routine childhood vaccination schedule in 2001 resulted in decreases in vaccine-type IPD and consequent decreases in all IPD among U.S. children, according to background information in the article. With the introduction of PCV7, one concern has been the potential for nonvaccine serotypes to emerge and diminish the disease prevention gains made through the use of PCV7.

Rosalyn J. Singleton, MD, MPH, of the Centers for Disease Control and Prevention (CDC), and colleagues evaluated IPD in Alaska children for evidence of the emergence of nonvaccine serotype disease. The researchers conducted a statewide population-based laboratory surveillance of invasive Streptococcus pneumoniae infections (such as pneumonia, meningitis, or bacteremia) from Jan. 1, 1995, through Dec. 31, 2006.

The authors found that in the three years after introduction of PCV7 (2001-2003), IPD decreased 67 percent among Alaska Native children younger than 2 years and 61 percent in non-Native Alaska children in the same age group. Between 2001-2003 and 2004-2006, IPD rates did not change for non-Native Alaska children younger than 2 years but increased 82 percent among Alaska Native children so that the overall IPD reduction in these children was only 39 percent during 2004-2006 compared to before vaccine introduction. Since 2004, the invasive pneumococcal disease rate caused by nonvaccine serotypes has increased 140 percent compared with the prevaccine period (from 95.1 per 100,000 in 1995-2000 to 228.6 in 2004-2006). During the same period, there was a 96 percent decrease in heptavalent vaccine serotype disease.

"The rapid success of PCV7 in Alaska has led to the near elimination of PCV7-serotype disease and elimination of a health disparity for types covered by the vaccine. However, for Alaska Native children there now exists a substantially elevated risk for IPD from serotypes not contained in PCV7. The demonstration of replacement IPD in Alaska Native children may signify a limit to the usefulness of the currently available vaccine and emphasizes the importance of development of extended valency vaccines or vaccines not dependent on serotype-specific prevention. These data also highlight the value of continued surveillance and other epidemiological investigations to monitor the effects of pneumococcal vaccines," the authors conclude.

In an accompanying editorial, Invasive Pneumococcal Disease: The Target is Moving,

Timothy R. Peters, MD, and Katherine A. Poehling, MD, MPH, of Brenner Children's Hospital at Wake Forest University School of Medicine, Winston-Salem, N.C., comment on the findings of Singleton and colleagues. "Pneumococcal serotype replacement is occurring in a subpopulation of highly vaccinated, especially vulnerable U.S. children. Although the efficacy of PCV7 remains high, changing pneumococcal serotype prevalence is causing increased rates of invasive disease. Surveillance of pneumococcal colonization and disease is important to the public health and is informing vaccine redesign. The target is moving. An adaptable vaccine strategy must also move to protect children worldwide and defend the idea that humankind will ultimately be free of pneumococcal disease."

Reference: JAMA. 2007;297:1784-1792.

Source: American Medical Association (AMA)