High frequency ultrasound to assess skin thickness in healthy adults

Intradermal immunization is gaining increased attention due to multiple factors: (1) intradermal (ID) vaccination has been shown to induce improved immunogenicity compared to intramuscular (IM) vaccination; (2) ID vaccination has been shown to have a dose-sparing potential over IM leading to a reduced vaccine cost and an increased availability of vaccines worldwide. However, the currently used Mantoux technique for ID injection is difficult to standardize and requires training. The aim of the study was (1) to assess the epidermal and dermal thickness at the proximal ventral and dorsal forearm (PVF & PDF) and deltoid in adults aged 18-65years (2) to determine the maximum penetration depth and needle characteristics for the development of a platform of medical devices suited for intradermal injection, VAX-ID™.

Mean thickness of the PVF, PDF and deltoid were measured using high-frequency ultrasound of healthy adults aged 18-65years. Correlation with gender, age and BMI was assessed using Mann-Whitney U Test, Spearman correlation and Wilcoxon Signed Ranks Test, respectively.

Results showed an overall mean skin thickness of 1.19mm (0.65-1.55mm) at the PVF, 1.44mm (0.78-1.84mm) at the PDF, and 2.12mm (1,16-3.19mm) at the deltoid. Thickness of PVF & PDF and deltoid were significantly different for men vs women (p_mean<0.001, <0.001, <0.001, and p_min<0.001, 0.012, <0.001, respectively). A significant association was found for age at the deltoid region (p<0.001). Skin thickness for PVF, PDF & deltoid was significantly associated to BMI (p<0.001).

Significant differences in skin thickness were seen for the PVF, PDF and deltoid region for gender, and BMI. Age only influenced the skin thickness at deltoid region. A needle length of 1.0mm is best option for intradermal injection at the dorsal forearm (NCT02363465).