Analysis of adverse events following immunization after immunization schedule adjustment for acellular DTaP combined vaccine among 6-year-old children in Hangzhou

In 2025, China adjusted national immunization schedule to administer a booster dose of acellular diphtheria-tetanus-pertussis combined vaccine (DTaP) to 6-year-old children, replacing the previously used diphtheria-tetanus combined vaccine (DT). Post-marketing safety surveillance of this newly implemented schedule is critical to evaluate the tolerability and safety of DTaP in this age group. To evaluate the epidemiological characteristics and safety of adverse events following immunization (AEFI) among 6-year-old children after administration of DTaP following the 2025 national immunization schedule adjustment in Hangzhou. To compare the incidence of AEFI between DTaP and DT. AEFI surveillance and vaccination data of 6-year-old children who received DTaP or DT from 2024 to 2025 in Hangzhou were collected. The total sample size was 239 480 doses of diphtheria-tetanus-containing vaccines. Descriptive statistics, chi-square test, and reporting odds ratio disproportionality analysis were used for statistical analysis. The overall reporting rate of AEFI following vaccination with diphtheria- and tetanus-containing vaccines among 6-year-old children in Hangzhou was 466.01 per 100,000 doses. The AEFI reporting rate for DTaP (833.58 per 100,000 doses) was significantly higher than that for DT (181.49 per 100,000 doses) (χ2 = 539.95, P < .05). AEFIs after DTaP vaccination were predominantly general reactions (99.31%), and no severe AEFI was reported. Disproportionality analysis detected positive signals only for local redness/swelling as a general reaction for both DTaP and DT. DTaP vaccination is safe and well-tolerated after the immunization schedule adjustment. Most AEFIs are mild general reactions including fever, redness, and induration, with reporting rates within the expected range and no obvious safety risks.