In the UK, primary care practitioners administer infant immunisations at 2, 3 and 4 months of age. Despite recommendations for use of a wide-long (23G, 25mm) needle, many UK practitioners immunise infants using a narrow-short (25G, 16mm) needle and uncertainty has arisen because of insufficient data to define best practice.
In a previous study, researchers from Oxford found that the wider-longer needle significantly reduced local reactions at 4 months of age. However, they did not know whether this was due to difference in needle length or gauge, or whether needle size affected vaccine immunogenicity.
To answer these questions, they carried out another trial comparing three needle sizes varying in length and diameter.
696 infants were randomly immunised with either a wide-long (23G, 25mm); a narrow-short (25G, 16mm); or a narrow-long (25G, 25mm) needle at 2, 3 and 4 months. Parents recorded local and general reactions for 3 days following each dose and antibody concentrations were measured 28-42 days after the third dose.
Local reactions decreased significantly with wider-longer over narrower-shorter needles.
Significantly fewer infants vaccinated with the longer needle experienced severe local reactions. Immunogenicity following injection with the longer needle was, however, comparable to that achieved with the shorter needle.
Comparisons between the same length, different gauge needles showed little difference in local reaction or immune response suggesting that needle length, rather than gauge, is responsible.
The results show a clear benefit of using the longer needle at each dose whilst achieving comparable immunogenicity, say the authors. They suggest that vaccine manufacturers and national policymakers use this evidence in recommendations for infant immunisation.
With increasing parental attention focused on the safety rather than the efficacy of vaccines, simple interventions, such as the use of a longer needle, that reduce local reactions should be welcomed, they conclude.