In a normally developing 3‑year‑old child, can intramuscular vaccines be administered in the deltoid muscle?

Deltoid Injections in 3-Year-Olds

Yes, intramuscular vaccines can be administered in the deltoid muscle of a normally developing 3-year-old child, provided the child has adequate deltoid muscle mass on visual and manual assessment. 1

Age-Based Site Selection

For children ≥12 months through 18 years, the deltoid becomes an acceptable primary injection site once adequate muscle mass is present. 1 Since your patient is 3 years old, they fall well within this age range where deltoid use is appropriate. 2, 1

• The anterolateral thigh was the preferred site for infants <12 months because it provides the largest muscle mass in that age group. 1
• After 12 months of age, the deltoid transitions to become an acceptable and often preferred site. 2, 1
• The anterolateral thigh remains an alternative option if deltoid muscle mass is insufficient. 1

Critical Assessment Required

You must visually and manually palpate the deltoid to assess muscle bulk before selecting this site—do not assume all 3-year-olds have adequate deltoid development. 1 This individual assessment is required for each child. 1

• If the deltoid appears underdeveloped on examination, continue using the anterolateral thigh even though the child is past 12 months of age. 1
• Research using ultrasound measurements confirms that by 25-36 months, deltoid muscle thickness averages 9.28 mm, which is adequate for intramuscular injection. 3

Proper Needle Specifications for a 3-Year-Old

Use a 22-25 gauge needle that is 7/8 inch to 1¼ inches long for deltoid injections in children ≥12 months. 2, 1 The needle length should be selected based on the individual child's muscle bulk. 1

• The needle must be long enough to reach the muscle tissue and prevent medication from seeping into subcutaneous tissue. 2, 4
• Using needles that are too short results in subcutaneous rather than intramuscular delivery, which reduces vaccine efficacy and increases local reactions. 1

Injection Technique

Insert the needle at a 90-degree angle perpendicular to the skin surface. 2, 1 This angle is critical because deviating from it can reduce medication efficacy or increase local adverse reactions. 2

• When administering multiple injections in the same limb, separate injection sites by more than 1 inch to allow clear differentiation of local reactions. 2, 1
• Never inject into the gluteal region due to risk of sciatic nerve injury and decreased vaccine immunogenicity. 1, 4

Common Pitfalls to Avoid

Do not assume universal deltoid adequacy without performing a visual and manual assessment of muscle bulk. 1 This is the most common error when transitioning from thigh to deltoid injections in toddlers.

• Avoid using the deltoid routinely before 12 months of age, as the thigh provides more reliable muscle mass in infants. 1
• Do not use inadequate needle length for the patient's body size, as this results in subcutaneous delivery. 1