Are influenza vaccines administered subcutaneously?

Influenza Vaccines Are NOT Administered Subcutaneously

Most influenza vaccines are administered intramuscularly, not subcutaneously, with the exception of one specific intradermal formulation (Fluzone Intradermal) and the intranasal live attenuated vaccine (LAIV). 1

Standard Route of Administration

Intramuscular Injection (Standard)

• Inactivated influenza vaccines (IIV) should be administered intramuscularly into the deltoid muscle for adults and older children, or the anterolateral thigh for infants and young children. 1, 2
• The recombinant influenza vaccine (RIV) is also administered intramuscularly. 1
• This is the preferred and recommended route by the Advisory Committee on Immunization Practices (ACIP) and CDC. 2, 3

Site Selection by Age

• Adults and children ≥4 years: Deltoid muscle of the upper arm 2, 3
• Infants and children <4 years: Anterolateral aspect of the thigh due to insufficient deltoid muscle mass 2, 3, 4

Alternative Routes (Specific Products Only)

Intradermal Administration

• Only Fluzone Intradermal is administered intradermally, preferably over the deltoid muscle, using a specialized delivery system included with the vaccine package. 1
• This is not the same as subcutaneous administration and requires a specific product formulation. 1

Intranasal Administration

• Live attenuated influenza vaccine (LAIV/FluMist) is administered intranasally only, not by injection. 1

Why Intramuscular Is Superior to Subcutaneous

Evidence Against Subcutaneous Administration

• Intramuscular injection produces better immune responses compared to subcutaneous injection, particularly for both influenza A strains (H3N2 and H1N1, p = 0.0016 and 0.003, respectively) in elderly adults. 5
• The superiority of intramuscular administration is especially pronounced in females, who show significantly greater serological responses with IM versus SC injection. 5
• Subcutaneous injection is associated with higher rates of local adverse reactions (37.4% vs. 17.4% for IM) without any safety benefit. 6
• Adjuvanted vaccines given subcutaneously induce unacceptable rates of injection site reactions. 7

Common Pitfall: Anticoagulation Concerns

Patients on Oral Anticoagulants

• Many physicians incorrectly use subcutaneous injection for patients on anticoagulation therapy, believing it reduces hemorrhagic complications. 6
• This practice is not evidence-based: A randomized controlled trial demonstrated that intramuscular influenza vaccination in anticoagulated patients causes no more side effects than subcutaneous administration and actually results in fewer local reactions. 6
• No major hemorrhage or significant bleeding complications occurred with intramuscular administration in anticoagulated patients. 6

Dosing Specifications

Standard Volumes

• 0.5 mL for most intramuscular products in children ≥36 months and adults 18-64 years 2
• 0.25 mL or 0.5 mL for Fluzone in children aged 6-35 months 4
• 0.7 mL for Fluzone High-Dose Quadrivalent in adults ≥65 years 2
• 0.1 mL for Fluzone Intradermal (the intradermal product, not standard IM vaccine) 1

Administration Technique

• Inject at a 90-degree angle into the muscle 2, 3
• Use appropriate needle length based on patient size and injection site per ACIP guidelines 2
• Aspiration is not required before injection because no large blood vessels exist at the recommended injection sites 2
• Clean the site with an alcohol swab before administration 4