What is the heterogeneity in the impact seen with pneumococcal conjugate vaccines telling us?

Vaccine
Volume 35, Issue 31, Pages 3797-3904 (5 July 2017)
http://www.sciencedirect.com/science/journal/0264410X/35/31

Commentaries
What is the heterogeneity in the impact seen with pneumococcal conjugate vaccines telling us?
Pages 3797-3800
William P. Hausdorff, Steve Black
Abstract
Pneumococcal conjugate vaccines have proven highly effective in decreasing invasive disease and pneumonia in young children. However, there is considerable geographic variability in the impact of these vaccines on other disease endpoints and in other age groups. Investigation of the possible causes of this variability would greatly improve our understanding of pneumococcal pathophysiology and stimulate the effort to design more broadly effective vaccines.