Once vaccines are manufactured in large quantities, the way they are delivered and administered is crucial for their success in preventing diseases. While injections have been the traditional method of vaccine administration, new delivery methods are being explored to improve population compliance, ease administration, and increase coverage.

Preparing the Vaccine

Before administering a vaccine, it needs to be adequately prepared and handled.

Selecting the Syringe and Needle

Choosing the right syringe is vital, and a new sterile needle and syringe should be used for each injection. Injectable vaccines can be delivered using either a 1-mL or 3-mL syringe as long as the prescribed dosage is given.

Needles should be suitable for the injection site and route. The size of the needle depends on factors such as the individual’s size, volume and viscosity of the vaccine, and injection technique. Typically, fine gauge needles (22-25 gauge) are used for vaccines that are not highly viscous.

Checking Expiration Dates

Before administration, the vaccine vial and diluent should be thoroughly inspected for damage or contamination. The expiration date printed on the vial or box should also be checked. Vaccines can be used until the last day of the month indicated by the expiration date, unless otherwise specified on the package labeling. Expired vaccines or diluents should never be used.

Diluent or Reconstitution

Some vaccines come in a freeze-dried form and require reconstitution with a liquid diluent, usually sterile saline or distilled water. Each diluent is specific to the corresponding vaccine in terms of volume, sterility, pH, and chemical balance. Using the wrong diluent renders the vaccine dose invalid and requires it to be repeated with the correct diluent.

Vaccines should be reconstituted just before administration. After reconstitution, the vial should be agitated or shaken to ensure the vaccine is thoroughly mixed and a uniform suspension is obtained before each dose is withdrawn.

Routes of Vaccine Administration and Sites

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The recommended route and injection site for each vaccine are determined based on clinical trials, experience, and theoretical considerations. This information is provided in the manufacturer’s product information for each vaccine.

Routes of Vaccine Administration

The routes of administration for most vaccines include:

• Oral (PO) Route – Recommended for Rotavirus vaccines, typhoid vaccines, and polio vaccines.

• Subcutaneous (subcut) Route – Subcutaneous injections are given just below the skin, in the fatty tissue below the dermis. The recommended subcutaneous sites for vaccine administration are the thigh (for infants younger than 12 months) and the upper outer triceps of the arm (for persons 12 months and older).

• Intramuscular (IM) Route – These injections are administered into muscle tissue below the dermis and subcutaneous tissue. All inactivated vaccines, except one formulation of meningococcal polysaccharide vaccine (MPSV4), are administered intramuscularly.

• Intradermal (ID) Route – Administered just below the skin or the dermal layer of the skin, typically in the deltoid region of the upper arm.

• Intranasal (NAS) Route – The live attenuated influenza vaccine is the only vaccine administered nasally.

Injection Sites

The recommended injection sites for vaccines are as follows:

• Left Vastus Lateralis (LVL) – Infants and toddlers lacking adequate deltoid mass.
• Right Vastus Lateralis (RVL)
• Left Deltoid (LD) – Toddlers, children, and adults.
• Right Deltoid (RD)
• Left Antero Lateral Fat or Thigh (LALT) – Infants and young children.
• Right Antero Lateral Fat or Thigh (RALT)
• Left Posterolateral Fat of Upper Arm (LPUA) – Children and adults.
• Right Posterolateral Fat of Upper Arm (RPUA)
• Left Fore Arm (LFA) – Intradermal tuberculin ppd skin test.
• Right Fore Arm (RFA)

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Read the manufacturer’s product information for each vaccine to determine the recommended route and site based on specific needs.

Newer Delivery Techniques

Recent advancements in vaccine delivery include the use of oral vaccines. The oral polio vaccine was the first of its kind and showed promising results, including increased administration ease. Oral vaccines offer several advantages, including easy administration, no risk of blood contamination, improved stability, reduced risk of freezing, less reliance on the cold chain, and decreased costs.

Needle-free injections, or jet injectors, have also been developed to reduce the risk of needlestick injuries to healthcare personnel and prevent improper reuse of syringes and needles.

Other methods, such as the microneedle approach, which involves vaccine delivery through the skin using pointed projections, and nasal sprays, are still in the developmental stages.

Additionally, newer techniques using liposomes for vaccine delivery and plasmids for cancer vaccines are being explored.

Special Situations for Vaccine Administration

Certain situations require special precautions when administering vaccines, including:

• Multiple Vaccinations: If more than one vaccine needs to be administered, it is desirable to inject each preparation at a different anatomical site. For infants and young children, if more than two vaccines are injected in a single limb, the thigh is preferred due to its larger muscle mass.

• Vaccinations in Patients with Bleeding Disorders: Patients with bleeding disorders may experience excessive bleeding or bruising at injection sites.

• Acute Vaccine Reactions: Although rare, severe allergic or other reactions may occur following vaccination. Thoroughly screening for contraindications and precautions prior to vaccination can often prevent such reactions.

Further Reading

• All Vaccine Content
• What are Vaccines?
• Vaccine History
• What is a Vaccine Breakthrough?
• What are the Main Causes of Vaccine Hesitancy?

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