Skin thickness in young infants and adolescents: Applications for intradermal vaccination

Abstract

As compared with standard intramuscular and subcutaneous vaccines, intradermal (ID) vaccines elicit a more potent immune response in both adults and children, with equivalent dosage or antigen dose sparing. Recently, various devices for ID injection have been developed; the length of needles ranges in 0.6-1.5 mm. However, skin thickness must be measured to determine optimal needle length for ID vaccines. Use of ID vaccines in infants and children is appealing because children require more vaccines than do adults; however, information on skin thickness in infants and children is limited. We used ultrasound echography to measure skin thickness in Japanese infants aged 2 months (n=78) and adolescents aged 13-15 years (n=82). Mean (range) deltoid and suprascapular skin thickness was 1.67 mm (1.16-2.39 mm) and 1.83 mm (1.24-2.60 mm), respectively, in infants and 1.81 mm (1.25-3.00 mm) and 2.43 mm (1.51-3.95 mm), respectively, in adolescents. Among infants who underwent re-measurement of skin thickness at age 6 months (n=11), mean deltoid skin thickness (1.84 mm) was significantly greater than at age 2 months (1.60 mm) (P<0.001). In contrast, no significant difference was observed in suprascapular skin thickness (1.79 mm vs. 1.67 mm, respectively; P=0.17). Gender was not associated with skin thickness in either age group. Skin thickness was positively correlated with body weight in adolescents (r=0.43, P<0.001 in deltoid region; r=0.30, P=0.01 in suprascapular region). In conclusion, this is the first study to evaluate skin thickness in different age groups of children, including at age 2 months. Skin thickness gradually increased from age 2 months to age 13-15 years, but no consistent trend was noted in analysis stratified by measurement site, gender, or age. These findings suggest that an appropriate length of ID device needle for infants and children is likely to be less than 1.2mm and a special device with shorter length of needle is warranted for infants and children.

Keywords: Adolescent; Deltoid; Infant; Intradermal injection; Skin thickness; Suprascapular.