Objective   To analyze characteristics of adverse events following immunization (AEFI) in Shenyang city from 2016 to 2019 and to provide evidences for assessing vaccination safety in the city.

  Methods  From National Immunization Program Information Management System, we extracted the data on all AEFI cases reported in Shenyang city during 2016 – 2019 and analyzed the data with descriptive epidemiology methods.

  Results   Among 5 548 250 doses of vaccines inoculated during the 4-year period in the city, totally 1 295 AEFI cases were reported and the reported annual incidence rate varied significantly (χ² = 74.46, P < 0.05), with an increase from 16.72/100 000 doses in 2016 to 32.51/100 000 doses in 2019. The most (91.64%) of the reported AEFI cases were common reactions and only 2.99% of the reported cases were abnormal reactions. There were 72.05% of the reported AEFI cases occurred among the children less than 2 years old and more cases were reported between May and July in a year. The reported incidence of AEFI was significantly different among administrative districts (χ² = 432.7, P < 0.05); the highest district-specific rate was 42.8/100 000 and the lowest was 25.2/100 000. The reported incidence of AEFI related to class A vaccines was significantly higher than that of AEFI related to class B vaccines (19.88/100 000 doses vs. 3.46/100 000 doses, χ² = 640.94; P < 0.05).

  Conclusion  The reported incidence of AEFI increased yearly from 2016 to 2019 in Shenyang city and the district-specific incidence differed significantly suggesting that the surveillance on AEFI needs to be improved in some regions.