The vaccine was produced by Shenzhen Kangtai Biological Products Co. which holds a > 50 % market share for this vaccine in China, and is used for cost-free vaccination of babies since 2005. The diseased babies were 2 to 8 months old. The reasons are unclear but one suspicion is that the vaccine was beyond its period of use. China SFDA suspended the use of the pertinent lot numbers.
China Bio news release, December 15, 2013