 This study found that IPD incidents decreased by 85% and 35% in children aged less than two years and two to less than five years, respectively from period 1, 1995 to 2004, to period 4, 2015 to 2017, with a 97% reduction in serotypes covered by the 7-valent vaccine. In period 4, 59% of the disease was caused by serotype 3 and was largely attributed to an Mb positive, novel ST6011 clone, indicating low efficacy of the 13-valent vaccine against infection by this serotype. This article was authored by Pat Lung-Ho, Piera Yintung Law and Susan S. Du.