Adverse reactions following upper arm vs. buttock DTaP vaccination in children: A retrospective observational study in Wuxi, China, 2020-2024.

Adverse reactions are closely associated with vaccination sites, making site selection vital for clinical administration of the diphtheria, tetanus, and acellular pertussis (DTaP) vaccine. This retrospective observational study enrolled 636,169 DTaP inoculations in Wuxi from 2020 to 2024. Adverse reaction data were extracted from the National Adverse Events Following Immunization Surveillance System of China, and dose data were obtained from the Jiangsu Province Vaccination Integrated Service Management Information System. We compared adverse reaction reporting rates stratified by overall incidence, severity, vaccine dose, and clinical manifestations, as well as constituent proportions of adverse reactions according to onset time between upper arm and buttock injection groups. The upper arm group had slightly higher reporting rates of adverse reactions and common reactions than the buttock group, at 23.88 (95% CI: 22.54-25.22) vs. 17.89 (95% CI: 15.56-20.21) and 23.13 (95% CI: 21.81-24.45) vs. 16.94 (95% CI: 14.68-19.20) per 10,000 doses, both p < .001, while rare reaction rates were comparable, at 0.75 (95% CI: 0.51-0.98) vs. 0.95 (95% CI: 0.41-1.48) per 10,000 doses, p = .473. Slightly elevated adverse reaction rates were also found in upper arm administration for the first and second doses. Redness and swelling, induration, and fever were the predominant adverse symptoms, all showing modestly elevated rates after upper arm injection. The adverse reactions at both sites were predominantly common reactions within expected range. Despite a slightly elevated risk of common reactions, upper arm injection may be the preferred site for DTaP vaccination for overall safety.