Use of same length needle for intramuscularly administered vaccines had been reported to cause under-and over-penetration among infants due to their different body weights and underlying variations in the fat and muscle thickness. Normative data regarding thigh compartment thickness are, however, lacking among neonates and infants aged ≤12 weeks particularly in low- and middle-incoming countries with high burden of low birth weight/growth restricted infants.
Present study investigated skin to muscle and skin to bone (STBD) distances of anterolateral thigh of babies (n = 300) aged ≤12 weeks (1–80 days) with different weight groups (<3 kg, 3–4 kg and >4 kg) by ultrasonography during their intramuscular vaccinations.
Overall, mean [standard deviation (SD)] STBD was 17.04 (2.66) mm with range of 10.60–23.30 mm. Stratifying by current body weight, mean (SD) STBD in infants weighing less than 3 kg was 14.39 (1.23) mm. For infants weighing between 3–4 kg and >4 kg, the mean (SD) STBD were 16.69 (1.43) mm and 17.04 (2.66) mm, respectively. Estimated safety (no risk of over-penetration) of 16 mm was observed in 57.33% (172) infants whereas 25 mm needle had 100% over-penetration risk in the study cohort. Current body weight of infants was a significant predictor of safe injection [area under the receiver operating characteristic (ROC) curve 0.95; 95% CI 0.92–0.97].
Our study offers objective normative measurements of anterolateral thigh for safe intramuscular vaccination in young infants especially for low birth weight and growth restricted infants in low- and middle-income countries.