Appropriate site and needle length depends on age, route of injection, and body mass. Most injected vaccines are administered by the intramuscular route.
Please refer for details to the Immunize.org handouts on administering intramuscular and subcutaneous vaccines to children and adults at www.immunize.org/catg.d/p2020.pdf and to adults only at www.immunize.org/catg.d/p2020a.pdf.
A summary of needle length and site selection by age is below.
For intramuscular injections (use a 22- to 25-gauge needle for all ages):
- For neonates (first 28 days of life) and preterm infants the anterolateral thigh should be used. A ⅝-inch needle usually is adequate to penetrate the thigh muscle if the skin is stretched flat between the thumb and forefinger and the needle is inserted at a 90-degree angle to the skin.
- The anterolateral thigh is preferred for infants younger than age 12 months. For the majority of infants a 1-inch needle is sufficient.
- For toddlers age 12 months through 2 years the anterolateral thigh muscle is preferred. The needle should be at least 1 inch long. The deltoid muscle can be used if the muscle mass is adequate.
- For children age 3 through 10 years, the deltoid muscle is preferred; the needle length for deltoid site injections can range from ⅝ to 1 inch on the basis of technique. The anterolateral thigh can also be used. In this case the needle length should be 1 inch to 1.25 inches.
- For adolescents 11 through 18 years, the deltoid muscle is preferred. The anterolateral thigh can also be used. For injection into the anterolateral thigh, most adolescents will require a 1-1.5-inch needle.
- For adults age 19 years and older, the deltoid muscle is preferred. The anterolateral thigh also can be used.
- For men and women who weigh less than 130 pounds (less than 60 kg), a ⅝-inch needle is sufficient to ensure intramuscular injection in the deltoid muscle if the injection is made at a 90-degree angle and the tissue is not bunched.
- For men and women who weigh 130–152 pounds (60–70 kg), a 1-inch needle is sufficient.
- For women who weigh 152–200 pounds (70–90 kg) and men who weigh 152–260 pounds (70–118 kg), a 1- to 1½-inch needle is recommended.
- For women who weigh more than 200 pounds (more than 90 kg) or men who weigh more than 260 pounds (more than 118 kg), a 1½-inch needle is recommended.
For subcutaneous injections (use a 23- to 25-gauge needle for all ages):
Subcutaneous injections are administered at a 45-degree angle, usually into the thigh for infants younger than age 12 months and in the upper-outer triceps area of people age 12 months and older. Subcutaneous injections may be administered into the upper-outer triceps area of an infant if necessary. A ⅝-inch needle length should be used for all ages.
More information on injection technique is in the ACIP “General Best Practices Guidelines for Immunization”, available at www.cdc.gov/vaccines/hcp/acip-recs/general-recs/administration.html.