[Evaluation of the protective effect of acellular DPT vaccine for booster immunization in 6-year-old children].

Objective: To evaluate the epidemiological protective effect of a booster dose of acellular DTP vaccine (DTaP) against pertussis in 6-year-old children. Methods: A retrospective cohort study was conducted to compare the incidence of pertussis in 6-year-old children who received DTaP versus DT vaccine boosters in 2023 over a two-year period from May 2023 to May 2025. The protective effect of the fifth dose of DTaP against pertussis in 6-year-old children was evaluated. Results: A total of 960 participants were enrolled in this study, including 480 children in the experimental group who received the fifth dose of DTaP vaccine and 480 children in the control group who received the DT vaccine booster. Baseline characteristics were balanced between the two groups. There were six confirmed cases of pertussis in the experimental group, with a reported incidence rate of 1.25%. In the control group, 14 pertussis cases were reported, with a reported incidence rate of 2.92%. The protective effectiveness(VE) of the DTaP vaccine against pertussis was 57.14% (95%CI:-10.59%-83.39%). For 6-year-old children who completed the booster immunization, the incidence data of pertussis were collected from the 14th day after vaccination (i.e., the study day 0). Based on the annual cumulative incidence rate, the VE of DTaP against pertussis at 6, 12, 18, and 24 months after vaccination was 100%, 63.80% (95%CI:-14.49%-88.55%), 64.59% (95%CI: 1.17%-87.31%), and 57.60% (95%CI:-10.80%-83.78%), respectively. In the DTaP group, the annual cumulative incidence rate of 12 to 24 months did not show a significant upward or downward trend (Z=-0.995, P=0.320). Conclusion: Boosting 6-year-old children with the DTaP vaccine provides measurable protection against pertussis. The protective efficacy is significant in the early stage (0 to 6 months) after vaccination, and it still remains effective at 12 to 24 months.