Shifting Pneumococcal Serotypes

Robert S. Baltimore, MD


Journal Watch 

In This Article

Abstract and Introduction


In Massachusetts, the incidence of invasive pneumococcal infection fell after introduction of the heptavalent conjugated pneumococcal vaccine, then stabilized because of infections from nonvaccine serotypes.


The serotypes of Streptococcus pneumoniae contained in the heptavalent conjugate pneumococcal vaccine (PCV7) were chosen because they were responsible for most of the pneumococcal infections in target populations. Do serotype shifts since the February 2000 introduction of PCV7 necessitate changes in the makeup of the vaccines?

Using records from the Massachusetts Department of Public Health, researchers — funded by the U.S. manufacturer of PCV7 — examined the serotypes underlying invasive pneumococcal disease (IPD) among children in that state from October 2001 through September 2007. Since 2003, approximately 90% of the state's children aged 19 to 35 months have received ≥3 doses of PCV7.

During the study period, 569 IPD cases were reported among children aged <18 years. Of the 433 isolates (74%) available for testing, only 15% were PCV7 serotypes. PCV7 serotypes accounted for 25% of the isolates from 2001–2002 but none from 2006–2007. A non-PCV serotype — 19A (JW Infect Dis Dec 2007, p. 89, and JAMA 2007; 298:1772) — was the most common and was the only serotype to show a significant increase from 2001–2002 to 2006–2007. During these 6 years, overall IPD incidence remained stable, because the drop in PCV7 serotype infections was offset by an increase in non-PCV7 serotype disease.


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.