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Vaccine components

Vaccine manufacture and composition is complex and tightly regulated to maximise safety. The safety of the individual components, and of the vaccine itself, must be demonstrated before a vaccine can be licensed and used in New Zealand.

What is in a vaccine?

  • Antigen
  • Adjuvant
  • Excipients
    • Preservatives
    • Stabili​sers
    • Buffe​rs
    • Surfactants
    • Solvents
    • Residuals
    • Diluents


All vaccines contain an active component (the antigen) which generates the protective immune response.


An adjuvant is an ingredient that helps retain the active component of the vaccine (antigen) at the injection site and attract inflammatory factors and immune system cells to the injection site to improve the immune response to the vaccine.

Some vaccines contain a tiny amount of aluminium salts, such as aluminium hydroxide, aluminium phosphate, and potassium aluminium sulphate (alum), to act as an adjuvant.

Aluminium is the third most abundant element present in the earth’s crust and found naturally in soil, plants, some foods we eat and water. Aluminium is added during the processing of some foods such as bread, and is also in the air we breathe.

We are born with some aluminium already stored in our body and continue to add to our aluminium stores through eating, drinking, receiving some vaccines and taking some medicines. Even though we regularly consume food and drinks containing aluminium throughout our lifetime, only a small amount of aluminium travels into the blood stream from digestion, the rest comes out in faeces. Most of the aluminium that enters our blood stream is quickly processed and removed by the kidneys in urine.

After more than 80 years use of aluminium containing vaccine and millions of doses given, there is no evidence that the aluminium in vaccines causes any long term health problems. Short term redness, pain and/or an area of hard swelling can occur where an aluminium containing vaccine has been given. Occasionally a small nodule can develop at the injection site. There is no evidence that the aluminium from intermittent vaccine doses cannot be removed by the body.


Excipients are all substances in the finished product, other than the active ingredients. Excipients may have been used during the manufacturing process or in the finished pharmaceutical product to maintain quality.


Preservatives stop unwanted contamination of a vaccine. They have been used in vaccines for many years. Very few serious adverse events have been associated with the use of these preservatives. The most commonly used preservative is 2-phenoxyethanol. 


2-phenoxyethanol is used in a range of cosmetics such as baby care products, eye and ear drops as well as vaccines. It is metabolised (broken down) and excreted by being exhaled, in the urine and in the faeces, and has little toxicity in humans.  Very high doses in animals can cause irritation.


Phenol is an aromatic alcohol infrequently used as a preservative in vaccines.


No thimerosal, also called thiomersal, is used in New Zealand vaccines. Historically, this mercury derived compound was used as a preservative in vaccines and other health care products internationally for many years.


Stabilisers stop chemical reactions from occurring in the vaccine and prevent the components from separating from each other or sticking to the vaccine vial during transportation and storage. 

Examples of stabilisers include sugars such as lactose and sucrose, amino acids such as glycine and monosodiumglutamate (salts of amino acids), proteins such as recombinant human albumin (Recombumin®) derived from baker’s yeast or fetal bovine (cow) serum and gelatin, partially hydrolysed collagen usually of porcine (pig) but can be of bovine origin.


Buffers serve to resist changes in pH, adjust tonicity and maintain osmolarity. The most commonly used buffer is sodium chloride (table salt).


Surfactants are a type of emulsifier. They assist particles remain suspended in liquid, preventing settling and clumping, by lowering the surface tension of the liquid. An example is polysorbate 80 (Tween 80®), made from sorbitol (sugar alcohol) and oleic acid (omega-9 fatty acid), which is also used in foods such as ice cream. Surfactants are also used in shampoos, toothpastes, inks and fabric softeners.


A solvent is a substance that dissolves another substance, creating a solution. The most common solvent used in everyday living, and vaccine manufacture, is water.


Residuals are the remaining minute quantities of substances that have been used during the manufacturing or production process of individual vaccines. Residuals depend on the process used, which may have involved cell culture mediums, egg proteins, yeast, antibiotics such as neomycin or streptomycin or inactivating agents such as formaldehyde. These substances are only present as traces and often measured as parts per million and parts per billion in the final vaccine formulation.

Animal derived products

Some people have concerns about animal derived products such as gelatin in vaccines. This may be for faith-based reasons or concerns about the safety of animal derived products. More information on animal derived products in vaccines can be found in the fact sheet Animal derived products and National Immunisation Schedule vaccines on our Written Resources webpage.


A diluent is a liquid used to dilute a vaccine to the proper concentration immediately prior to administration. This is usually sterile water.


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Last updated: Jul 2020