Chích vắc-xin

Intramuscular vaccines are administered into the muscle layer of tissue at a 90° angle. Muscle contains a vast amount of blood vessels resulting in increased blood supply which enables the vaccine to disperse easily. In addition, muscles contain dendritic (antigen-presenting) immune cells that initiate a long-lasting immune response. Intramuscular vaccines tend to have fewer side-effects other than redness and pain at the injection site, which are usually mild and short lived.

Subcutaneous vaccines are administered into the subcutaneous, or fatty layer beneath the skin at a 45° angle. Vaccines designed for subcutaneous administration are absorbed at a slower and more constant rate as there is less blood supply in subcutaneous tissue than muscle.

Intradermal vaccines are administered into the outer layers of skin, between the epidermis and the dermis at a 5-15° angle. The epidermal and dermal layers contain many different cells including the antigen-presenting cells (APC’s) that are thought to play a significant role in mediating an efficient and protective immune response to specific vaccines. The 3 main APC’s are macrophages, dendritic cells and B cells. APC’s present specific antigens to particular cells in the immune system that are responsible in eliciting an immune mediated response that in turn creates memory cells and antibodies.

Intradermal vaccination is a unique method of vaccine delivery which requires specific training to ensure vaccine safety and efficacy.

Oral vaccines activate immune cells in the mucousal membranes lining the gastrointestinal tract which is beneficial in protecting against diseases that affect the gut.

Depending on the vaccine, oral vaccines can come in either tablet or liquid formulation. Liquid vaccines recommended for oral administration should never be injected. Oral vaccines available in tablet form should not be chewed or broken.

Please note, if an infant receiving an oral vaccine spits out a small amount of the dose of vaccine it is still considered a valid dose and doesn’t need repeating. If they spit out most of the dose of vaccine within minutes of receiving it, a repeat dose should be administered at the same visit.

The recommended injection site is the middle third of the vastus lateralis (anterolateral thigh).

To locate the correct anatomical site for injection:

• ensure the infant’s leg is completely exposed
• locate the upper and lower anatomical landmarks- greater trochanter of femur and patella
• draw an imaginary line between the 2 landmarks down the front of the thigh
• then imagine the thigh is divided into thirds
• the correct injection site is located in the middle third and on the outer aspect of the imaginary line (see images below).

Where only two vaccines are scheduled it is recommended to give one vaccine into each thigh. If more than two vaccines are recommended at the one visit, two vaccines may be given into each thigh ensuring they are separated by 2.5 cm (refer to images below). When administering more than one vaccine into the same thigh, it is important to consider the reactogenicity of each vaccine. Those that are considered more reactogenic should be in different thighs where possible. For example, meningococcal B (Bexsero®) is frequently associated with increased local site reactions.

In some circumstances where the thigh cannot be used (e.g. congenital limb malformations, active eczema or hip brace placement) the deltoid may be used (refer to the recommended site for injection in children ≥ 12 months for guidance).

The recommended injection site is the deltoid (upper arm).

To locate the correct anatomical site for injection:

• expose the arm completely from the top of the shoulder to the elbow; remove shirt or clothing if needed
• locate the upper and lower anatomical landmarks- acromion (shoulder tip) and the muscle insertion of the deltoid (deltoid tuberosity)
• draw an imaginary inverted triangle below the shoulder tip, using the identified landmarks (see images below)
• the site for injection is halfway between the acromion and the deltoid tuberosity, in the middle of the deltoid muscle (triangle).

Two or more vaccines may be given into the same deltoid ensuring they are separated by 2.5 cm (refer to images below). When administering more than one vaccine into the same deltoid, it is important to consider the reactogenicity of each vaccine. Those that are considered more reactogenic should be in different deltoids where possible. For example, meningococcal B (Bexsero®) and pneumococcal polysaccharide (Pneumovax® 23) are frequently associated with increased local site reactions.

Utilising the anterolateral thigh may also be required in this age group (e.g. congenital limb malformations, history of auxillary clearance, active eczema or insufficient spacing available). In these circumstances, there is a preference for administering the least reactogenic vaccines via this site (refer to the recommended site for injection in children ≤ 12 months for guidance).

The recommended sites for intradermal administration are the volar (inner) surface of the mid-forearm or over the deltoid region over where the deltoid muscle inserts into the humerus.

The deltoid region on the left arm is specifically recommended for BCG administration in any age groups as administration at this site minimises the risk of keloid scarring.

• Use a short (10mm) 26-27 gauge needle with a short bevel and a 1ml insulin syringe
• Wear protective eye wear when administering BCG vaccine as eye splashes can ulcerate
• Identify the correct injection site (see Table 1 above)
• Stretch the skin between a finger and your thumb
• Insert the bevel into the dermis with the bevel facing upwards, to a distance of approx. 2mm. The bevel should be visible through the epidermis

You should feel resistance as you inject, if you don’t, the needle may be in subcutaneous tissue. If the injection is not intradermal, withdraw the needle and repeat at a new site. When given correctly, an intradermal injection should raise a blanched bleb.