Evidence-based Medicine Workbook

Objective To compare rates of local reactionsassociated with two needle sizes used to administerroutine immunisations to infants.Design Randomised controlled trial.Setting Routine immunisation clinics in eight generalpractices in Buckinghamshire.Participants Healthy infants attending for thirdprimary immunisation due at 16 weeks of age: 119infants were recruited, and 110 diary cards wereanalysed.Interventions Immunisation with 25 gauge, 16 mm,orange hub needle or 23 gauge, 25 mm, blue hubneedle.Main outcome measures Parental recordings ofredness, swelling, and tenderness for three days afterimmunisation.Results Rate of redness with the longer needle wasinitially two thirds the rate with the smaller needle(relative risk 0.66 (95% confidence interval 0.45 to0.99), P = 0.04), and by the third day this haddecreased to a seventh (relative risk 0.13 (0.03 to0.56), P = 0.0006). Rate of swelling with the longerneedle was initially about a third that with the smallerneedle (relative risk 0.39 (0.23 to 0.67), P = 0.0002),and this difference remained for all three days. Ratesof tenderness were also lower with the longer needlethroughout follow up, but not significantly (relativerisk 0.60 (0.29 to 1.25), P = 0.17).Conclusions Use of 25 mm needles significantlyreduced rates of local reaction to routine infantimmunisation. On average, for every five infantsvaccinated, use of the longer needle instead of theshorter needle would prevent one infant fromexperiencing any local reaction. Vaccinemanufacturers should review their policy of supplyingthe shorter needle in vaccine packs.