Vaccine ingredients


General information

The key ingredient in all vaccines is the active ingredient. This is the part that challenges the immune system so that it makes antibodies that can fight the disease. Apart from this, the main ingredient in vaccines is water. Most injected vaccines contain 0.5 millilitres of liquid, in other words a few drops. All other ingredients weigh a few milligrams (thousandths of a gram) or even less.

Vaccine ingredients can look unfamiliar. However, it is important to remember that many of the substances used in vaccines are found naturally in the body. For example, many vaccines contain salts based on sodium and potassium, which are essential for life. People may think of formaldehyde as a man-made chemical, but in small quantities it is also found naturally in the bloodstream.

All vaccine ingredients are present in very small quantities, and there is no evidence that any of them cause any harm in these amounts. If you look up some vaccine ingredients on the internet you may read that they could be harmful, but most of them are present in vaccines in amounts that are completely normal for our bodies. Even common salt (sodium chloride), which is essential for normal functioning of the body, is harmful in large quantities.

Active ingredients

These are the parts of the vaccine made from viruses or bacteria (also called ‘antigens’). They challenge the immune system so that it makes antibodies to fight the disease. Vaccines contain tiny quantities of active ingredients – just a few micrograms (millionths of a gram) per vaccine. To give some idea of how small these quantities are, one paracetamol tablet contains 500 milligrams of the drug. This is several thousand times more than the quantity of the active ingredient you would find in most vaccines. Hundreds of thousands of individual vaccines could be made from a single teaspoon of active ingredient.

Some vaccines contain whole bacteria or viruses. In these cases the bacteria or viruses will either be severely weakened (attenuated) so that they cannot cause disease in healthy people, or killed altogether (inactivated). Many vaccines contain only parts of viruses or bacteria, usually proteins or sugars from the surface. These stimulate the immune system but cannot cause disease.

Compared to the number of viruses and bacteria in the environment that our bodies have to deal with every day, the amount of active ingredient in a vaccine is very small indeed. Most bacterial vaccines contain just a few proteins or sugars from the relevant bacterium. By contrast it is estimated that 100 trillion bacteria live on the skin of the average human being, each of them containing many thousands of proteins which constantly challenge our immune systems.

A few vaccines in the UK schedule are made using recombinant DNA technology. This is a technique that uses bacterial or yeast cells to manufacture the vaccine. A small piece of DNA is taken from the virus or bacterium that we want to protect against. This is inserted into other cells to make them produce large quantities of active ingredient for the vaccine. For example, to make the Hepatitis B vaccine, part of the DNA from the HepB virus is inserted into the DNA of yeast cells. These yeast cells are then able to produce one of the surface proteins from the HepB virus, and this is purified and used as the active ingredient in the HepB vaccine. The HPV vaccine and part of the MenB vaccine are made using a similar technique.

Only one vaccine used in the UK contains genetically modified organisms (GMOs).

More detail about active ingredients can be found on each of the pages about individual vaccines.

A few products used in vaccine manufacture are a risk to some people, even in trace amounts, because they can cause allergic reactions (for example, egg proteins and antibiotics). These products are always clearly stated on vaccine information leaflets. Other items are present in such tiny quantities that they do not pose a risk.

A complete list of vaccine ingredients can be found on the Patient Information Leaflet (PIL) and Summary of Product Characteristics (SPC) sheet for each vaccine. See the list of PILs and SPCs on our links page.

Added ingredients

These are products such as aluminium salts that help to improve the immune response to vaccines, or products that act as preservatives and stabilisers (for example, gelatine or human serum albumin). These are listed on vaccine information leaflets as ‘excipients’ (inactive ingredients). Like vaccines, most of the medicines we use also contain excipients. Most vaccines do not now contain the preservative thiomersal (also called thimerosal).

Aluminium (an adjuvant)

Many vaccines contain aluminium salts such as aluminium hydroxide, aluminium phosphate or potassium aluminium sulphate. They act as adjuvants, strengthening and lengthening the immune response to the vaccine. Aluminium salts slow down the release of the active ingredient from the vaccine once it is injected, and stimulate the immune system to respond to the vaccine. They also absorb protein well, and stop the proteins in the vaccine sticking to the walls of a container during storage.

The amount of aluminium present in vaccines is extremely small - less than 2 milligrams of the salts, and less than a milligram of actual aluminium. After vaccination there is a temporary increase in the amount of aluminium in the body, but this is not a lasting effect. The body gets rid of most of the aluminium in just a few days. There is no evidence that this causes any risk to babies and children. Aluminium is a very common metal in the environment, and it is also found naturally in breast milk, formula milk, some foods and drinking water. Small amounts therefore accumulate naturally in children’s bodies.

Two studies from 2002 and 2011 compared the impact of aluminium from diet and vaccines in infants. Both of these found that the total amount of aluminium absorbed from both sources is significantly less than the recommended safe maximum amount. Read the abstracts of these studies here (2002) and here (2011) .

Rarely, aluminium adjuvants may cause small itchy lumps (granulomas) to form at the injection site. A 2014 Swedish study found that this happened in a small number of children (fewer than 1 in 100) after vaccination with the 5-in-1 vaccine (Infanrix) and pneumococcal vaccine (Prevenar). Granulomas are not dangerous but can be irritating and last for months or even years. The study found that children with granulomas often developed an aluminium contact allergy. However, most children recovered from their symptoms.

It is now considered that there is no relationship between aluminium and Alzheimer’s disease. There is no evidence to suggest that exposure to aluminium increases the risk of dementia.

Aluminium salts are found in these vaccines used in the UK:

The Children's Hospital of Philadelphia has a useful page which lists the actual amounts of aluminium found in vaccines used in the USA .

Thiomersal, also called thimerosal in the US (a preservative)

Thiomersal is a mercury-based preservative used in tiny quantities in some vaccines to prevent the growth of bacteria and fungi which can contaminate from the environment when the vaccine is opened.

Most single-dose vaccines do not contain thiomersal because they are used only once and so there is very little risk of contamination. However, some vaccines are produced in multi-dose vials. There are two reasons for this: they are cheaper, and they are easier to produce quickly in large quantities in the event of an epidemic. Tiny quantities of thiomersal are often used in multi-dose vaccines to stop them becoming contaminated once they are opened.

Thiomersal was removed from UK vaccines between 2003 and 2005, and is no longer found in any of the childhood or adult vaccines routinely used in the UK. Before 2005, thiomersal was present in diphtheria- and tetanus-containing vaccines, as well as hepatitis B vaccine and some flu vaccines. It was not used in the MMR vaccine, the Hib vaccine, the MenC vaccine, the oral polio vaccine or the BCG vaccine. Since 2005, thiomersal has only been present in non-routine vaccines such as hepatitis B, and occasionally in some of the annual inactivated flu vaccines. Thiomersal was present in the Swine Flu (H1N1) vaccine Pandemrix, used in the 2009-10 and 2010-11 flu seasons in the UK. However, it is not present in any of the annual flu vaccines currently in use in the UK.

In the US, UK and Europe, thiomersal was removed from vaccines as a precaution. This was in line with the global goal of reducing environmental exposure to mercury from all sources. However, there was no evidence that thiomersal in vaccines caused harm. Thiomersal contains a compound called ethyl mercury, but concern about mercury in the environment has centred on a different compound called methyl mercury, which accumulates in the food chain and in the human body. Studies have shown that the ethyl mercury in thiomersal does not appear to accumulate in the bodies of even very small babies. It is cleared from the blood in 30 days, and the evidence suggests that it is passed out in the baby’s stool (poo). See more information about these studies.

The World Health Organization (WHO) and the European Medicines Agency (EMA, previously EMEA) have both stated that there is no evidence of risk from thiomersal in vaccines. Read the WHO statement and the EMA statement . There is also detailed information about the safety of thiomersal on the US Food and Drug Administration's pages .

A recent Australian study of over a million children found no evidence of a link between thiomersal in vaccines and autism development.

Gelatine (a stabiliser)

Gelatine derived from pigs is used in some live vaccines as a stabiliser to protect live viruses against the effects of temperature. Gelatine in vaccines is highly purified and hydrolysed (broken down by water), so it is different from the natural gelatine used in foods. For example, very sensitive scientific tests have shown that no DNA from pigs can be detected in the nasal flu vaccine (Fluenz). These tests show that the gelatine is broken down so much that the original source cannot be identified.

There have been a tiny number of cases of allergic reaction to vaccines containing gelatine (about one case for every 2 million doses of vaccine). People with a known allergy to gelatine should seek expert advice before receiving vaccines containing gelatine.

Members of Muslim or Jewish religious communities may be concerned about using vaccines that contain gelatine from pigs (porcine gelatine). According to Jewish laws, there is no problem with gelatine or any other animal substance if it is used in a product that does not go into the mouth. Some Muslim leaders have also ruled that the use of gelatine in vaccines does not break religious dietary laws, because it is highly purified and it is also injected rather than ingested (eaten). This issue was addressed by a Public Health England statement issued in October 2013. In 2001 the World Health Organization consulted with over 100 Muslim scholars, who judged that it was acceptable for Muslims to receive vaccines containing gelatine. See their statement here .

Gelatine is found in these vaccines used in the UK:

  • one of the MMR vaccines (MMRVaxPro). (Priorix, the other MMR vaccine used in the UK, does not contain gelatine.)
  • the Nasal Flu vaccine (Fluenz). However, very sensitive scientific tests have shown that no DNA from pigs can be detected in Fluenz. These tests show that the gelatine is broken down so much that the original source cannot be identified.
  • the shingles vaccine (Zostavax)
  • one of the chickenpox vaccines (Varivax). (Varilrix, the other chickenpox vaccine used in the UK, does not contain gelatine.)

More information can be found in the NHS leaflet 'Vaccines and porcine gelatine' .

Human Serum Albumin (a stabiliser)

Human serum albumin is the most common protein found in human blood. It is currently used in very small quantities as a stabiliser in one of the chickenpox vaccines used in the UK (Varilrix). It comes from blood donors who are screened, and the manufacturing process takes away any risk of passing on viruses from the serum. No viral diseases have ever been linked to the use of human serum albumin.

Recombinant human serum albumin (a stabiliser)

One of the MMR vaccines used in the UK, MMRVaxPro, contains a very small amount of recombinant human serum albumin (0.3 mg per dose). Recombinant albumin does not contain any human or animal products. The albumin is produced by cells (such as yeast cells) that have had the gene for human albumin inserted into them. The cells are then able to generate large quantities of human serum albumin without any need to extract it from human blood.

Sorbitol and other stabilisers

Sorbitol is produced naturally in the human body and also found in fruit and berries. It is commonly used as a sweetener in foods and drinks. In vaccines it is used in small quantities as a stabiliser. There may be up to 15 milligrams of sorbitol in the MMR vaccines used in the UK (MMR VaxPro and Priorix). Sorbitol may also be present in one of the chickenpox vaccines (Varilrix). Sorbitol is usually harmless, but people with an allergy to sorbitol, or with rare inherited problems of fructose intolerance, should not receive vaccines containing sorbitol.

Other products used in very small quantities as stabilisers in vaccines include:

  • Sugar (sucrose)
  • Lactose (milk sugar)
  • Mannitol, similar to sorbitol – see above
  • Glycerol, a common non-toxic substance often used as a food additive
  • Medium 199, a solution which contains amino acids (the building blocks of proteins), mineral salts and vitamins
  • Monosodium glutamate, a salt made from the amino acid glutamine
  • Urea, a harmless organic compound found in the human body


Polysorbate 80 is a common food additive used in several vaccines as an emulsifier (to hold other ingredients together). Compared to its use in foods, there is very little polysorbate 80 in vaccines.

Taste improvers

The oral rotavirus vaccine (Rotarix) contains about a gram of sugar (sucrose) to give it a pleasant taste. This is about a quarter of a teaspoon of sugar.

Products used in the manufacture of the vaccine

Unlike food product or other drug product listings, everything used in the production of a vaccine will be listed under ‘excipients’. However, many of the items listed do not actually remain in the finished vaccine.


Antibiotics are used during the manufacturing process of some vaccines to stop bacteria growing and contaminating the vaccine. However, antibiotics which commonly cause allergic reactions (such as penicillins, cephalosporins and sulphonamides) are not used in vaccines.

Traces of five antibiotics may appear in the following vaccines used in the UK. People with a known allergy to any of these antibiotics should ask for expert advice before receiving these vaccines.

Egg Proteins (Ovalbumin)

Egg allergy is quite common in children under 5, and much more common in children than in adults. Around 60,000 children in the UK have egg allergies. In the UK schedule, both the Nasal Flu Vaccine (Fluenz Tetra) and the Inactivated Flu Vaccine may contain traces of egg proteins. This is because the flu virus is grown on fertilised hens' eggs. Egg-free flu vaccines have been developed but so far they have not been consistently available. Others are also being developed. However, the Joint Committee on Vaccination and Immunisation has now advised that most children with an egg allergy can be safely vaccinated with the nasal flu vaccine (Fluenz Tetra). This is because the ovalbumin content is very low. The only exception is children who have a history of severe anaphylaxis to eggs which has previously needed treatment in intensive care. These children should be referred to specialists for immunisation in hospital. This advice is based on a recent study called SNIFFLE which tested Fluenza Tetra on several hundred children with egg allergy. See more information about the SNIFFLE study and an information sheet from Public Health England showing the ovalbumin content of flu vaccines in the 2015/16 season .

In the past, people with an egg allergy were advised not to receive the MMR vaccine. Advice on this changed more than ten years ago. The measles and mumps viruses are grown on a culture which contains chick embryo cells (not on eggs). This means that there is not enough egg protein in the MMR vaccine to cause allergic reactions, so children with severe egg allergies can safely receive the MMR. Doctors have carefully studied this issue and confirmed that there is no increased risk of reactions to the MMR vaccine in children who are allergic to eggs.

Other non-routine vaccines, such as yellow fever vaccine, may also contain egg proteins. Those with egg allergy should always ask about egg protein content before receiving a vaccine.

Yeast Proteins

Yeast is used in the production of the HPV vaccine (Gardasil) used in the UK. Department of Health advice is that the HPV vaccine can be given to yeast allergy sufferers because the final product does not contain any yeast.

A tiny quantity of yeast protein may remain in the Hepatitis B vaccine (HBVaxPro), but there is no evidence that this can cause allergic reactions.


Latex (natural rubber) is used in the packaging of some vaccines. For example, the needle tip of the syringe may be protected with a latex bung. This is a risk for people who have a severe allergy to latex (one that causes an anaphylactic reaction), and they should talk to a doctor before receiving a vaccine. People who have less severe latex allergies (for example, a history of contact allergy to latex gloves) are not at risk from latex in vaccine packaging.

In the UK the product information leaflets of the following vaccines state that latex is used in the packaging:

Formaldehyde and Glutaraldehyde

Formaldehyde is an organic compound found naturally in many living things. It is used in the production of some vaccines to inactivate toxins from bacteria and viruses (for example, poliovirus, Hepatitis B antigen, and diphtheria and tetanus toxins). It is possible that tiny traces may remain in the Hepatitis B vaccine (HBVaxPro), one of the Pre-school Booster vaccines (Repevax), and the Teenage Booster vaccine (Revaxis). However, formaldehyde breaks down quickly in water (and most of the vaccine is water).

The human body produces and uses formaldehyde as part of the process of metabolism. The amount of natural formaldehyde in a 2-month-old infant’s blood (around 1.1 milligrams in total) is ten times greater than the amount found in any vaccine (less than 0.1 milligrams). A pear contains around 50 times more formaldehyde than is found in any vaccine.

Glutaraldehyde is a similar kind of organic compound which is also used to inactivate toxins from bacteria used in vaccines. A trace may remain in one of the Pre-school Booster vaccines (Repevax).

Acidity Regulators

Like all other living things, viruses and bacteria need to be kept at the right pH (acid/alkaline level). A number of different products are used in very small quantities to help keep the pH balance right while vaccines are being manufactured. These products include:

  • Salts based on potassium phosphate and sodium phosphate. These are common and harmless. As well as keeping the pH balance, they also help to keep the fragments of active ingredient suspended in the water, so that they do not settle out. A product called Hanks’ Salts, which contains these salts and others, is sometimes used.
  • Disodium adipate, also commonly used as a food additive.
  • Succinic acid, which is involved in several chemical processes in the body.
  • Sodium hydroxide and hydrochloric acid: when these are used they react to form water and harmless salts, and so do not appear in the final vaccine in their original form.
  • Histidine, an amino acid found in almost every protein in the human body.
  • Sodium borate (borax): a few micrograms (millionths of a gram) may remain in the Hepatitis B vaccine (HBVaxPro) and the HPV vaccine (Gardasil). This amount is too small to cause any harm.
  • Trometamol, also used in the manufacture of other medicines.

Human Cell-lines

For some vaccines, the active ingredient has to be grown in laboratories on cultures that contain human cell-lines. This is because the viruses are specific to humans and will only grow in human cells. For vaccines used in the UK, only the viruses for the rubella part of the MMR vaccines (MMRVaxPro and Priorix) and for the shingles vaccine and chickenpox vaccines (Zostavax, Varivax and Varilrix) are grown in human cell-lines. Once grown, the viruses are purified several times to remove the cell culture material.

The cell-lines used (called WI-38 and MRC-5) were started in the 1960s using small quantities of lung cells taken from two aborted foetuses. The abortions were legal and agreed to by the mothers, but they were not performed for the purpose of vaccine development. The original foetal cells have long since disappeared. Because these cell-lines still exist nearly 50 years later, no other foetuses are needed to make human cell-lines for growing these vaccine viruses.

Some people may have concerns about using a vaccine produced using foetal tissue, even though the original cells do not exist any longer. In 2005 the Vatican’s Pontifical Academy for Life issued a statement called ‘Moral reflections on vaccines prepared from cells derived from aborted human foetuses’. This statement says that they believe it is wrong to make vaccines using human cell-lines derived from foetuses, and that there is a ‘moral duty to continue to fight’ against the use of such vaccines and to campaign for alternatives. However, it also states that if the population is exposed to ‘considerable dangers to their health’ through diseases such as rubella (German measles), then ‘vaccines with moral problems pertaining to them may also be used on a temporary basis’.

Animal Cell-lines

Viruses for some vaccines are grown in laboratories on animal cell-lines. Again, this is because viruses will only grow in human or animal cells. In the UK schedule this applies to these vaccines:

Viruses for these vaccines are grown on Vero cells. This is a cell-line started in the 1960s using a few kidney cells from an African green monkey.

The measles and mumps parts of the MMR vaccines (MMRVaxPro and Priorix) are grown on a culture which began with cells taken from a chick embryo.

As with human cell-lines, the original cells have long since disappeared. There is no risk that animal diseases will be transmitted by vaccines grown on animal cell-lines.

Genetically Modified Organisms (GMOs)

The only vaccine in the UK schedule which contains GMOs is the Nasal Flu vaccine (Fluenz). The viruses for flu vaccines are usually made by injecting two flu virus strains into an egg and letting them recombine naturally to make new strains. Researchers then look through all the new viruses to see which one has the features they are looking for to make this year’s vaccine. The viruses used to make Fluenz are custom-made by putting together individual genes that will give the right features. This is a quicker and more accurate process.

Bovine products

‘Bovine products’ refers to any product that is derived from a cow or calf (such as bovine serum, which comes from cow's blood). Some sources state that bovine products may be present in the media that are used to grow the viruses or bacteria that are used to make the components of some vaccines. However, the Vaccine Knowledge Project has not been able to find any documentation of the use of bovine products in vaccines manufactured for use in the UK. Bovine products are not listed on any of the Summary of Product Characteristics sheets (SPCs) for any vaccine currently used in the UK.

Other growing media

Some bacteria do not need to be grown on human or animal cells. Instead they can be grown on cultures that are rich in proteins, vitamins and salts. Cultures that are often used in the production of vaccines are Medium 199, Eagle Medium and Minimum Essential Medium.

Further information

If you have questions about any of the other ingredients or excipients used in vaccines, ask your GP for advice, or contact the vaccine manufacturer named on the vaccine's Patient Information Leaflet (PIL) or Summary of Product Characteristics (SPC) sheet. See the list of PILs and SPCs on our links page.

An article from 2003 giving further detailed information on vaccine ingredients can be found here .

The information on this page is based on the best information that we can find from the available literature.

Page last updated: 
Monday, February 20, 2017