Objective: To analyze the epidemiological characteristics, associated factors, and vaccine effectiveness of two pertussis cluster outbreaks in two primary schools in Yangzhong City in 2025, so as to provide evidence for school based epidemic prevention and control. Methods: From August 26 to 30, 2025, a pertussis questionnaire was administered to the epidemic affected classes of two primary schools (school A and school B) in Yangzhong City. A descriptive epidemiological retrospective analysis was used to characterize the pertussis cluster outbreaks in Yangzhong City from March to July 2025. A 1∶5 matched case control study (79 cases, 395 controls) was performed. Multivariate Logistic regression was used to identify associated factors, and the clinical symptom incidence rates, types of pertussis containing vaccines, and timeliness of vaccination were compared between groups using Fisher s exact test. Results: From March to July 2025, a total of 79 pertussis cases were reported in the two schools, with attack rates of 1.33% and 1.01%, respectively. Cases were predominantly aged 7-8 years (85.37% in school A, 73.68% in school B), and the main clinical manifestation was productive cough (63.29%). The pneumonia incidence rate among hospitalized cases ( 57.14 %) was higher than that among nonhospitalized cases(4.17%)(Fisher s exact test, P <0.01). The interval from the last dose to onset was concentrated at 6 to <7 years (44 cases). Logistic regression showed that children exposed to secondhand smoke in daily life ( OR = 3.86 ), those whose desk mates or front/back desk mates took leave due to cough ( OR =4.67), and those whose dining table mates or front/back table mates took leave due to cough ( OR =3.67) had significantly higher risks of pertussis (all P <0.05). A high proportion of both the case group and the control group received the acellular DTaP vaccine (97.47% and 96.96%, respectively),while a low proportion received the pentavalent vaccine (1.27% and 3.04%, respectively). Additionally, one case received only three doses of the acellular DTaP vaccine.The difference in vaccine type distribution between the two groups was not statistically significant (Fisher s exact test, P =0.31). Conclusions The outbreaks represent breakthrough infections under high vaccine coverage. Close contact and secondhand smoke exposure are the main risk factors. A booster immunization strategy with diphtheria-tetanus-pertussis vaccine should be implemented for school aged children.