Abstract: Objective To analyze the surveillance data of adverse events following immunization (AEFI) with diphtheria, tetanus and acellular pertussis combined vaccine (DTaP) in Anyang before and after adjustment of the immunization schedule so as to provide references for reducing the incidence of AEFI. Methods Using the Chinese Disease Control and Prevention Information System, the AEFI reports of DTaP in Anyang from January 1, 2024 to December 31, 2025. were collected. Data on DTaP vaccines during the same period was collected via the Henan Provincial Immunization Program Information Management System. The reporting rates and clinical characteristics of AEFI of DTaP vaccines were analyzed and compared. Results Before the adjustment, the reported incidence rate of DTaP AEFI in Anyang was 829.46 per 100 000 doses, and those of common or abnormal reactions were 828.65 per 100 000 doses and 0.81 per 100 000 doses, respectively, compared with 882.78 per 100 000 doses, 882.21 per 100 000 doses and 0.57 per 100 000 doses after the adjustment. There were no significant differences in the reported incidence of AEFI before and after the adjustment(χ²=2.419,P=0.120). Before and after the vaccination program was updated, the reporting rates of fever, local redness and swelling, and local induration rose significantly with the increase in vaccination doses (P<0.001). With the extended time interval between vaccination and onset of adverse events, the proportions of local redness and swelling, and local induration increased. Conclusion Since the immunization schedule was updated, AEFI of DTaP in Anyang is mostly common reactions, and abnormal ones are rare. DTaP vaccines are relatively safe. However, vaccination needs to be standardied and AEFI monitoring enhanced.

Key words: Diphtheria, Tetanus and Acellular Pertussis Combined Vaccine(DTaP), Immunization Schedule, Adverse Events Following Immunization(AEFI), Surveillance, Safety