Echographic measurement of skin thickness in adults by high frequency ultrasound to assess the appropriate microneedle length for intradermal delivery of vaccines

Skin thickness (epidermis–dermis) across the deltoid, suprascapular, waist and thigh as possible body sites for a new microdelivery system for intradermal (id) inoculation were evaluated using 20 MHz ultrasound echography in 205 women and 137 men aged 18–70 years, in three ethnic groups: Caucasian, Asian and Black. Mean skin thickness was 2.54 mm at the suprascapular, 2.02 mm at the deltoid, 1.91 mm at the waist and 1.55 mm at the thigh. A 1.5 mm microneedle length inserted perpendicularly to the skin surface would ensure the administration of the antigen into the dermal layer, irrespectively of subject gender, age, ethnicity and BMI. The deltoid, suprascapular and waist are the most appropriate body sites.