Vaccine administration: A guide to selecting needle gauge and length

Date published: July 2026

Why is needle selection important?

• Needle selection should be based on the route of vaccine administration, recipient’s factors (e.g. age, muscle mass), and immunizing agent.
• This is to reach the appropriate tissue site (dermis, subcutaneous tissue or muscle), to optimize the immune response and reduce the risk of injection site reactions.
  • For intramuscular injections, the needle must be long enough to reach muscle but not involve underlying nerves, blood vessels, or bone. When needles are too short to reach muscle, vaccine may be inadvertently injected into more superficial tissue such as dermis and subcutaneous tissue, resulting in increased inflammation, induration or granuloma formation.
• The use of safety-engineered needles and syringes (e.g. built in sharps injury protection mechanisms) is preferred and, in many jurisdictions, mandated by law to reduce risk of injury.

General considerations

There are several things you should consider when administering a vaccine, including choosing the right needle gauge and length:

1. Determine the vaccine(s) that is required based on:
   • patient’s age
   • medical and vaccination history
   • provincial or territorial vaccination schedule
2. Determine administration route based on vaccine product.
   • List of vaccines and route of administration: Contents of immunizing agents authorized for use in Canada: Canadian Immunization Guide.
3. Determine if the vaccine requires mixing with a diluent or adjuvant.
4. Determine the appropriate:
   • dosage
   • site of injection
   • needle gauge
   • needle length
5. Administer the vaccine(s).

For more information on vaccine administration practices, including infection prevention and control: Vaccine administration practices: Canadian Immunization Guide.

Additional resource: Vaccine administration: A guide to landmarking.

Routes of administration

There are 3 routes of vaccine administration by injection:

Figure 1 : Descriptive text

A cross section of the different layers of the skin is depicted, progressing from the most superficial to the deepest layer: epidermis, dermis and hypodermis. Beneath these, a layer of muscle is depicted. Blood vessels (vein and artery) are depicted within the dermis and hypodermis. For intramuscular injection, a needle is shown inserted at a 90-degree angle (perpendicular to the skin) into the layer of muscle below the hypodermis (subcutaneous tissue). For subcutaneous injection, a needle is shown inserted at a 45-degree angle into the hypodermis (subcutaneous tissue). For intradermal injection a needle is shown inserted at a 5- to 15-degree angle into the dermis.

Selection of needle based on the route of administration