NEW YORK (Reuters Health) – Although quite rare, local reactions to the fifth dose of diphtheria/tetanus/acellular-pertussis (DTaP) vaccine in children are more likely when the vaccine is injected into the arm rather than the thigh, researchers report.

Writing in the March issue of Pediatrics available online February 7, Dr. Lisa A. Jackson, with the Group Health Research Institute in Seattle, Washington and colleagues note that the risk of local reactions increases with successive doses of DTaP vaccine. Local reactions are relatively common after the fifth DTaP vaccination, and sometimes lead to a physician visit. “Those medically attended reactions likely represent a more severe subset of adverse events after vaccination,” the authors suggest.

To investigate factors affecting the risk of medically attended local injection-site reactions, the team analyzed data on children 4-6 years of age who received a DTaP vaccination from 2002 through 2006.

“Among the 233,616 children in the study population, 1017 (0.4%) had a confirmed medically attended local reaction to the fifth dose of the DTaP vaccine,” the investigators report.

They found that the reaction rate was 47.4 per 10,000 vaccinations in the arm compared with only 32.1 per 10,000 vaccinations when given in the thigh (p<0.001). On multivariate analysis, the relative risk for a local reaction in the arm versus the thigh was 1.78.

Dr. Jackson and colleagues conclude, “The thigh should be considered an acceptable site of injection for this vaccination.”

Reference:
The Fifth Dose of Diphtheria and Tetanus Toxoids and Acellular Pertussis Vaccine
Pediatrics 2011;127.