 A formalin-inactivated EV71 vaccine Human Diploid cell, KMB-17 Cell has been finished phase I, II and III clinical trials and licensed by SFDA in China at Dec. 3, 2015. Based on the results of clinical trials, the protective efficacy of inactivated EV71 vaccine is 97 against HFMD caused by EV71. The phase IV clinical trial has been carried out from July 2016. The purpose of phase IVb is to evaluated the safety and efficacy of the inactive EV71 vaccine in large scale population of Chinese children from 6 to 71 months old in Hubei Province, China. 