Randomized trial using ultrasound to assess intramuscular vaccination at a 60° or 90° needle angle.

Objective: Globally, recommendations differ on the ideal angle of needle insertion to ensure vaccinate deposition in muscle for optimal safety and immunogenicity. This study aimed to compare the level of vaccinate deposition during vaccination, using two different needle angles (60° and 90°), in young children, adolescents and adults.

Methods: In this randomized cross-over study, two doses of a licensed hepatitis vaccine, were administered to study participants, at a 60° or 90° angle using a fixed template. Ultrasonography was performed with a Philips iu22 ultrasound system. Real time clips and hard copies of images were recorded showing the injection and level of deposition of the vaccinate. Reactogenicity at the site of administration was assessed by participants/parents.

Results: Nineteen participants were enrolled including children, adolescents and adults. Of the total 38 injections performed, 29 (76%) were confirmed by ultrasound as intramuscular (IM), 3 (8%) as not IM, and 6 (16%) unknown. For vaccinations visualised and administered at 60°, 87% (13/15) were intramuscular vs 94.1% (16/17) for those administered at 90°. A body mass index (BMI)≤25 was associated with a higher likelihood of IM injection compared to BMI>25 (p=0.038). There were no differences in reactogenicity for either 60° or 90° angle of administration.

Conclusion: For the majority of vaccinees, a 60-90° angle of vaccine administration is appropriate for IM deposition of vaccinate. The likelihood of intramuscular deposition is reduced for individuals with a BMI>25. The increasing rates of obesity globally highlight the importance of tailoring vaccination procedures accordingly.