What are the current recommendations for the site, side, needle size, and length for intramuscular injections, including vaccinations, in patients of different ages and body mass?

Current Recommendations for Vaccine Administration: Site, Side, Needle Size, and Length

Preferred Injection Sites by Age

For infants under 12 months, use the anterolateral aspect of the thigh as the primary site; for toddlers, older children, and adults, use the deltoid muscle when adequate muscle mass is present. 1, 2

Infants (<12 months)

• Primary site: Anterolateral aspect of the thigh provides the largest muscle mass 1, 2
• Alternative site: Deltoid muscle can be used when multiple vaccines must be administered at the same visit 1
• Needle specifications: 7/8 to 1 inch length, 22-25 gauge 1, 2
• Technique: Insert at 90-degree angle; bunch the muscle and direct the needle inferiorly along the long axis of the leg 1

Toddlers and Children (12 months to 18 years)

• Primary site: Deltoid muscle if adequate muscle mass is present 1, 3, 2
• Alternative site: Anterolateral thigh remains an option 1, 2
• Needle specifications: 7/8 to 1¼ inches length, 22-25 gauge 1, 2
• For the thigh in toddlers, use a longer needle (typically 1 inch) compared to infants 1, 2

Adults (>18 years)

• Primary site: Deltoid muscle is the recommended site for routine intramuscular vaccination 1, 3, 2
• Alternative site: Anterolateral thigh can be used 1, 2
• Needle specifications: 1 to 1½ inches length, 22-25 gauge 1, 3, 2

Weight-Based Needle Selection for Optimal Deltoid Injection

For patients with higher body mass, longer needles are essential to ensure intramuscular rather than subcutaneous delivery. 4, 5

Evidence-Based Weight Thresholds

• Patients <60 kg: 0.625 inch (16 mm) needle is appropriate 4, 6
• Patients 60-70 kg: 1 inch (25 mm) needle provides optimal intramuscular delivery 4, 6
• Patients 70-118 kg (males) or 70-90 kg (females): 1 inch (25 mm) needle is adequate 4
• Patients >118 kg (males) or >90 kg (females): 1.5 inch (38 mm) needle is required to achieve 96% successful intramuscular inoculation 4

Arm Circumference as a Practical Guide

• Males with arm circumference ≥35 cm: Use a longer needle to ensure intramuscular delivery 5
• Females with arm circumference ≥30 cm: Use a longer needle to ensure intramuscular delivery 5
• These thresholds ensure at least 5 mm penetration into muscle tissue 5

Optimal Deltoid Injection Site Location

The ideal injection site is 4 cm distal to the posterolateral corner of the acromion, which is more posterior and inferior than traditional recommendations. 4, 7

Precise Anatomical Landmarks

• Position the injection site at the midpoint of the deltoid muscle, midway between the acromion and deltoid tuberosity 7
• Have the patient place their hand on the ipsilateral hip; place your index finger on the acromion and thumb on the deltoid tuberosity, then inject at the midpoint 7
• This site minimizes risk of axillary nerve injury and overpenetration while maximizing successful intramuscular delivery 4, 7
• Avoid more anterior and superior sites, which are associated with higher rates of overpenetration 4

Critical Sites to Avoid

Never use the buttock for routine vaccination due to risk of sciatic nerve injury and decreased vaccine immunogenicity. 1, 3, 2

• Gluteal injection is associated with decreased immunogenicity of hepatitis B and rabies vaccines, likely due to inadvertent subcutaneous or deep fat tissue injection 1, 3
• If the buttock must be used for large-volume passive immunization, use only the upper outer quadrant with the needle directed anteriorly 1

Injection Technique Specifications

Angle of Insertion

• Intramuscular injections: Insert at 90-degree angle perpendicular to the skin surface 1, 2
• Subcutaneous injections: Insert at 45-degree angle into the thigh (infants <12 months) or upper-outer triceps area (persons >12 months) 1
• Intradermal injections: Insert parallel to the long axis of the forearm with bevel facing upward 1

Needle Length Principles

• The needle must be long enough to reach muscle mass and prevent vaccine from seeping into subcutaneous tissue 1, 2
• The needle must not be so long as to involve underlying nerves, blood vessels, or bone 1, 2
• Inadequate needle length results in subcutaneous rather than intramuscular administration, potentially reducing vaccine efficacy 3, 2

Aspiration Technique

• Aspiration before injection is not necessary according to CDC guidelines, as no data support this as a required procedure 2
• If aspiration is performed and blood appears in the needle hub, withdraw and select a new site 1

Multiple Vaccine Administration

When administering multiple vaccines, use different anatomic sites and separate injections by at least 1-2 inches if using the same limb. 1, 2

• Each vaccine preparation should be administered at a different anatomic site when possible 1
• The thigh is preferred over the arm when multiple injections must be given in the same limb due to greater muscle mass 1
• Adequate separation (1-2 inches apart) prevents local reactions from overlapping 1, 2
• Document the location of each injection in the medical record 2

Evidence Quality Considerations for Needle Length

High-Quality Evidence for Longer Needles in Infants

• 25 mm needles (either 23 G or 25 G) produce significantly fewer local reactions compared to 16 mm needles in infants receiving DTwP vaccines 8
• For every 25 infants vaccinated with a 25 mm rather than 16 mm needle, one fewer infant will experience severe local reactions (extensive redness and swelling) 8
• For every 5-6 infants vaccinated with a 25 mm rather than 16 mm needle, one fewer infant will experience non-severe local reactions 8
• Immune response is comparable between 25 mm and 16 mm needles 8

Gauge Considerations

• Using a wider gauge 23 G needle may slightly reduce procedural pain and crying duration compared to 25 G needles, though the clinical significance is minimal 8
• Needle gauge selection (22-25 gauge) should be based on the size of the muscle and volume to be administered 1

Common Pitfalls to Avoid

• Using the buttock for routine vaccination increases risk of sciatic nerve injury and reduces vaccine immunogenicity 1, 3, 2
• Selecting inadequate needle length for patient body size results in subcutaneous delivery and reduced efficacy 3, 2, 5
• Injecting too anteriorly or superiorly in the deltoid increases overpenetration risk 4
• Using a 1.5 inch needle in patients <118 kg leads to high rates of overpenetration 4
• Failing to bunch the muscle in infants may result in inadequate muscle penetration 1