Objective  To evaluate the safety of a homemade inactivated enterovirus type 71 (EV71) vaccine in a phase IV clinical trial in a large population of children and to provide references for extensive inoculation of the vaccine.

  Methods  Totally 25 995 healthy children aged 6 – 71 months were vaccinated with a self-paid inactivated EV71 vaccine under their parents′ informed consent between August 2016 and December 2017 in Chaoyang district of Beijing city. The two doses of the vaccination were administered with intramuscular injection at upper arm deltoid. Immediate adverse reactions within 30 minutes of the vaccination were observed; general and local reactions and other adverse events within 30 days after the inoculation were recorded via follow-up telephone interview and the reporting of the children's statutory guardians. We graded the observed adverse events (local red/swollen and induration and fever) following the vaccination with references to the Guidelines for Classification of Adverse Events for Preventive Vaccine Clinical Trials issued by National Food and Drug Administration. We also calculated the incidence rate of the adverse events simultaneously.

  Results  Totally 1 730 adverse events occurred following vaccinations of 52 260 doses of homemade inactivated EV71 vaccine among all the children inoculated, with an incidence rate of 3.31%. Of all the abnormal reactions observed, 1 178, 516, and 36 were general, local, and other adverse events, with the incidence rate of 2.25%, 0.99%, and 0.07%, respectively. Among all the adverse events reported, 362, 537, and 36 were classified as grade I, II, and III adverse events, with the incidence rate of 0.69%, 1.03%, and 0.07%. No grade IV or higher, rare, and extremely rare adverse events were reported. All the reported adverse events were cured with medication or outpatient treatment.

  Conclusion  The homemade EV71 vaccine is of good safety when inoculated in a large population of children.