Abstract
Introduction: Access to effective vaccination is an important way to protect against infectious diseases. The Aotearoa-New Zealand immunisation handbook on safe and effective vaccination practice recommends a 38-mm needle length for intramuscular deltoid injections in very large individuals, using clinical judgment to ensure needle length is appropriate to reach muscle. It is not clear how vaccinators implement this guidance in practice.
Aim: This study aimed to explore vaccinators' needle-length selection practice for big-bodied people and their views on a prototype arm circumference tool to guide needle choice.
Method: Vaccinators working with Māori and Pacific communities were recruited via researchers' networks to take part in one of six in-person focus groups in the Wellington region, Horowhenua district, and Tairāwhiti region (August-October 2025). Data were analysed qualitatively using a reflexive thematic approach.
Results: Twenty-five primary care-based vaccinators with varied roles and experience participated. Themes identified in the discussion included prioritisation of patient-centred care, influences on decision making (familiarity with guidance, training, workflow and equipment), and strengthening practice in these areas. The prototype tool was viewed positively, with discussion highlighting its potential to improve familiarity with arm size and needle-length criteria. Practical, workflow, and patient-centred considerations were raised, with particular focus on the importance of communicating use of the tool in a sensitive manner.
Discussion: Ensuring adequate supply and availability of 38-mm needles, along with clear guidance and education, are essential to support vaccinators' clinical judgement and effective vaccine delivery to big-bodied people. Use of an arm circumference assessment tool could strengthen vaccinators' decision making and help standardise needle length.