Which injection site is commonly used for vaccines in infants?

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In infants, vaccines are most safely given intramuscularly into the vastus lateralis, located in the anterolateral thigh. This muscle provides reliable, well-developed tissue for injection in babies, and its location keeps the needle away from major nerves and blood vessels that run near the buttocks or back of the thigh. The deltoid is too small and underdeveloped in infants, making it difficult to administer vaccines into proper muscle. The gluteal regions, including the dorsogluteal and gluteus medius sites, carry a higher risk of hitting the sciatic nerve and can be inconsistent because the muscle and underlying fat distribution vary in infants, increasing the chance of subcutaneous rather than intramuscular injection. For these reasons, the anterolateral thigh’s vastus lateralis is the standard site for infant vaccines, often using a small needle (about 5/8 inch) to ensure the injection reaches the muscle.