Recently, except of inactivated vaccine, several EV71 vaccine candidates have been evaluated in animals but no final results of clinical trials, such as attenuated vaccine, subunit vaccine. 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 IVc is to evaluated the immunogenicity of the inactive EV71 vaccine in large scale population of Chinese children (from 6 to 71 months old) in Hubei Province, China.