Background: The effects of needle size on immune response and adverse reactions from childhood immunizations are unknown. To address this lack of data, Diggle and colleagues compared three types of needles used for routine childhood immunizations.

The Study: The study was conducted in 18 English general practices. Children scheduled to receive their first immunization series (combined diphtheria, tetanus, pertussis, Haemophilus influenzae type b, and serogroup meningococcal C vaccine) were randomly assigned to one of three needle size groups: a wide, long needle (23 gauge [0.6 mm diameter], 25 mm); a narrow, short needle (25 gauge [0.5 mm diameter], 16 mm); or a narrow, long needle (25 gauge, 25 mm).

All the immunizations were performed using the same technique. Parents were asked to document their child's reaction to the immunization, including redness, hardness, or swelling at the injection site; reactions to touching the injection site or moving the injected limb; use of analgesics; and any other suspected reactions. To assess immune response, a blood sample was drawn from each child 28 to 42 days after the third vaccination in the series.

Results: Of the 696 infants enrolled, 240 were randomized to wide, long needles; 230 to narrow, short needles; and 226 to narrow, long needles. The infants in each group did not differ in any significant variables. Although immunogenicity was not significantly different, the average immune response was higher in infants in the wide, long needle group, and it was lowest in the narrow, short needle group. The differences in immunogenicity were greatest for the meningococcal C vaccine.

Overall, local reactions at the injection site were reported for 61 percent of infants. Significantly fewer local reactions were reported in the wide, long needle group. Over the three-dose series, the relative reduction ranged from 22 to 54 percent. The size of the reaction also was smaller, but this difference was not statistically significant. Differences in reactivity were only apparent for the first vaccine dose. Eleven infants were withdrawn from the study because they had injection site reactions; 10 of these infants were in the narrow, short needle group.

The three groups of infants did not differ in reported systemic reactions or use of analgesics, and the infants in the long needle groups did not differ significantly in immunogenicity. The narrow, long needle was associated with lower local reactivity compared with the wide, long needle; however, both had similar systemic reactivity.

Conclusion: The authors conclude that local reactions from routine childhood immunizations are significantly reduced with no change in immunogenicity or increase in systemic reactions when wide, long needles are used. This may be because the longer needle more consistently reaches the muscle layer.