Objective: Local reactions are relatively common after the fifth diphtheria-tetanus-acellular pertussis vaccination, but factors associated with an increased risk of those reactions are not well defined. The objective of this study was to assess the relationship between needle length and injection site on the risk of local reactions to the fifth diphtheria-tetanus-acellular pertussis vaccination administered in the context of usual clinical care.
Methods: In this prospective assessment, parents reported signs and symptoms of adverse events for 7 days after vaccination. The relative risk of adverse events in relation to needle length (16 or 25 mm) and injection site (arm or thigh) was estimated in multivariate analyses that adjusted for age, gender, and BMI. RESULTS; Of the 1315 study participants, 89% were vaccinated in the arm, and 67% were vaccinated with a 25-mm needle. Among children vaccinated in the arm, use of the shorter 16-mm needle was associated with a significantly higher risk of any redness, > or = 5 cm of redness, persistent redness on day 2, and pain compared with vaccination with a 25-mm needle. Similar trends among the smaller group of children vaccinated in the thigh were also suggested but were not statistically significant. In analyses that were restricted to children vaccinated with a 25-mm needle, vaccination in the thigh versus arm was associated with a substantially lower risk of > or = 5 cm of redness and a significantly lower risk of swelling and any itching but not with any difference in the risk of pain, irritability, or change in activity.
Conclusions: These findings suggest that a 25-mm needle should be used for the fifth diphtheria-tetanus-acellular pertussis vaccination regardless of injection site and that vaccination in the thigh is an option that may be considered by parents and providers who would like to decrease the risk of local reactions characterized by redness and swelling.