[Study on the incidence of adverse reactions following single versus simultaneous administration of the domestic diphtheria, tetanus, and acellular pertussis combined vaccine after immunization schedule adjustment].

This study compared the incidence of adverse reactions following single versus simultaneous administration of the domestic diphtheria, tetanus and acellular pertussis combined vaccine (DTaP) after the immunization schedule adjustment in 2025. Using active surveillance methods, children aged 2 months to 6 years who received domestic DTaP in Shapingba District, Chongqing, from January to March 2025 were enrolled and divided into a single-administration group and a simultaneous-administration group. Adverse reaction data were collected through follow-up at 30 minutes, 7 days, and 30 days post-vaccination. The Chi-square test or Fisher's exact test was used to compare differences between the two groups. A total of 4 887 doses of follow-up were completed. The overall incidence of adverse reactions in the single-administration and simultaneous-administration groups was 12.12% (218/1 799) and 11.59% (358/3 088), respectively, with no statistically significant difference (χ2=0.30, P=0.583). No statistically significant differences were found between the two groups regarding the type, severity, time of onset, number of vaccination doses, or manufacturer of adverse reactions (all P>0.05). The incidence of adverse reactions following simultaneous administration of domestic DTaP with one or two other vaccines showed no significant difference compared with single administration (all P>0.05). In conclusion, following the 2025 adjustment to the domestic DTaP immunization schedule, simultaneous administration does not increase the risk of adverse reactions in children aged 2 months to 6 years, supporting the promotion of simultaneous vaccination strategies.