Editorial Commentary:Changing Epidemiology of Invasive Pneumococcal Disease: A Complicated Story

Abstract

jugate vaccine into the WMA population in Arizona. This study is very beneficial to our understanding of the dynamics of pneumococcal epidemiology in general and of the impact, both positive and negative, that vaccine introduction may have in a population. The study performed by Lacapa et al. [2] was an observational study and compared rates of disease in the time period before vaccine introduction with rates in the time period after vaccine introduction. One of the key observations of the study was that the incidence of invasive disease due to the 7 serotypes covered in the vaccine was reduced substantially in this highrisk population. The observed 92% reduction in the rate of infectious pneumococcal disease among high-risk children aged !5 years is consistent with the reductions observed in other studies. However, the rate of disease among vaccinated WMA children still remains higher than that among the general population. There are 2 reasons for this. First, given the higher initial rate of disease, a 92% reduction in the rate of disease still leaves a substantial disease burden in the population. Second, prior to vaccine introduction, the proportion of overall invasive disease due to the 7 serotypes covered in the vaccine was only 56.2% among WMA children, compared with ∼90% in the general population. The reasons for this difference are not known, but the difference is consistent with both the variability of coverage of the 7-valent conjugate vaccine globally and with changes in serotype distribution observed over time in the Native American population and other populations globally. Although other vaccines that contain 10 and 13 pneumococcal serotypes are in development and would provide broader coverage, until we better understand the reasons that serotype distributions vary geographically and over time, strategic vaccine design will be hampered.