Most injected vaccines contain 0.5 millilitres, in other words a few drops. Almost all of this is water. Other ingredients weigh just a few milligrams (thousandths of a gram). To give some context, one paracetamol tablet weighs 500 milligrams. The 'active ingredients' in the vaccine are present in even smaller quantities - a few micrograms (millionths of a gram).
In addition to the main ‘active ingredient’ (a virus, bacterium, or a substance derived from these), vaccines may contain:
- adjuvants, which are substances that improve the effectiveness of the vaccine (such as aluminium salts).
- stabilising agents (such as gelatin or human serum albumin).
Most vaccines now do not contain the preservative thiomersal (also called thimerosal).
Somewhat confusingly, the list of vaccine ingredients will, unlike food product listings, also include all products used during the production process, even if they do not remain in the finished product. These may include formaldehyde, antibiotics, egg proteins, yeast proteins, human cell-lines, or animal cell-lines.
Vaccine ingredients can look scary because we are not used to seeing them listed in products intended for use in humans, but this does not mean they are dangerous. For example, people may think of formaldehyde as a chemical used to preserve dead bodies, and do not know that it is also found naturally in the bloodstream.
A complete list of ingredients can be found on the Patient Information Leaflet and Summary of Product Characteristics sheet for each vaccine. See the list on our links page.
Aluminium is used in vaccines in the form of salts such as aluminium hydroxide, aluminium phosphate, and potassium aluminium sulphate. Aluminium salts are an important component of vaccines since they act as adjuvants, strengthening and lengthening the immune response to the vaccine.
Aluminium can be harmful in large quantities. However, the amount of aluminium present in vaccines is very small (less than 2 milligrams of the salts, and less than a milligram of actual aluminium). Although vaccination does result in a temporary increase in the amount of aluminium in the body of infants, this is not a lasting effect, since 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 also found naturally in breast milk, formula milk, some foods and drinking water, and small amounts accumulate in children’s bodies as a result. 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. The 2011 study concluded that 'the benefits of using vaccines containing aluminium adjuvant outweigh any theoretical concerns'.
It is now thought unlikely that there is a relationship between aluminium and Alzheimer’s disease. There is currently no evidence to suggest that aluminium exposure increases the risk of dementia.
Thiomersal (also called Thimerosal)
Thiomersal is a mercury compound used as an antiseptic and antifungal agent. It is not found in any of the childhood vaccines routinely used in the UK, but is still widely used outside of Europe and America in vaccines produced in the cheaper multi-dose format. Fluvirin, one of the adult flu vaccines used in the UK in 2013-2014, may contain traces of thiomersal left over from the manufacturing process.
The World Health Organization (WHO) has stated that there is no evidence of risk from thiomersal in vaccines. Read the full WHO statement on thiomersal in vaccines.
Gelatin derived from pigs is used in certain vaccines to protect the viruses against the effects of temperature. The only vaccines containing gelatin in the UK routine schedule are the MMR vaccine and the nasal flu vaccine (Fluenz). There have been a tiny number of cases of allergic reaction to vaccines containing gelatin (around 1 in 2 million cases). People with a known allergy to gelatin should seek expert advice before receiving vaccines containing gelatin.
Religious groups such as Muslims and Jews may be concerned about using vaccines that contain gelatin from pigs. Many religious leaders have ruled that this use of gelatin does not break religious dietary laws. Gelatin in vaccines is highly purified and hydrolysed (broken down by water), so it is different from natural gelatin. It is also injected rather than ingested (eaten). See the October 2013 Public Health England statement about this. In 2001 the World Health Organization consulted with over 100 Muslim scholars, who judged that it was acceptable for Muslims to receive vaccines containing gelatin. See their statement here.
Human Serum Albumin
Human serum albumin, derived from human blood, is used as a protein stabilizer in the MMR vaccine (0.3mg/dose). It is derived from screened donors, and the manufacturing process eliminates any risk of transmitting viruses. No viral diseases have ever been associated with the use of human serum albumin.
Formaldehyde is an organic compound used in the production of some vaccines. It is used to inactivate poliovirus, HepB antigen, and diphtheria and tetanus toxins. It is possible that tiny traces may remain in the HepB vaccine, 5-in-1 DTaP/IPV/Hib, pre-school booster 4-in-1 DTaP/IPV, and teenage booster Td/IPV vaccines. The human body produces formaldehyde itself as part of the metabolism process. The amount of natural formaldehyde in a 2-month-old infant’s blood (around 1.1 milligrams) is ten times greater than the amount found in any vaccine (less than 0.1 milligrams).
Antibiotics are used during the manufacturing process of some vaccines to prevent bacterial contamination. However, antibiotics which have been associated with allergic reactions (such as penicillins, cephalosporins and sulphonamides) are not used in vaccines. Three vaccines may contain a trace of neomycin: the MMR vaccine, one of the Pre-school Booster vaccines used in the UK (Repevax), and the shingles vaccine. People with a known allergy to this specific antibiotic should seek expert advice before receiving these vaccines. Repevax may also contain traces of streptomycin and polymyxin b, and the Nasal Flu vaccine (Fluenz) may contain a trace of gentamicin.
Around 1 in 20 people are allergic to egg, and egg allergy is much more common in children than in adults. There are two vaccines in the current UK schedule which may contain egg proteins:
- The MMR vaccine: the measles and mumps viruses are grown on a culture which contains chick embryo cells. There is only a tiny amount of residual egg protein found in the MMR vaccine - approximately 40 picograms (that is 0.000 000 000 04g). This is not enough to cause allergic reactions, and children with severe egg allergies can safely receive the MMR.
- The nasal flu vaccine (Fluenz): the flu virus is grown on fertilised hens' eggs and the vaccine may contain residues of the egg proteins. At the moment there are no data on the use of Fluenz in children with an egg allergy. They should therefore be given an alternative vaccine, either an egg-free inactivated flu vaccine (if available) or, following specialist medical advice, a vaccine with a very low albumin content.
Most of the annual flu vaccines for adults also contain egg proteins, as the virus is often grown on fertilised hens’ 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 is not used in the production of any of the vaccines used in the UK routine schedule, except for the Gardasil HPV vaccine. UK Department of Health advice is that Gardasil can be given to yeast-allergy sufferers because the final vaccine product does not contain any yeast.
A tiny quantity of yeast protein may remain in Hepatitis B vaccines, though there is no evidence that this can cause allergic reactions.
Cell culture is the process by which cells derived from living organisms are grown and reproduced in a controlled laboratory environment. In the manufacture of some vaccines, such as the MMR, cultures containing human cell-lines are used to grow a virus. This is because the virus is specific to humans and will not grow in any other medium. The cell-line used in the production of the rubella element of the MMR is grown on a cell culture called WI-38, while the shingles vaccine (Zostavax) is grown on MRC-5. These cultures originated in lung cells taken from two different aborted foetus in the 1960s (the foetuses were not aborted for this purpose). None of the original cells remain in the culture. It is possible that traces of the cell-culture may remain in the vaccines.
Some people have concerns about using a vaccine produced using foetal tissue. The Vatican’s position on the matter is that ‘it is acceptable to use vaccines developed from abortions that were carried out decades ago, because immunizations play a vital role in protecting life by preventing illness and death’ (Statement by the Pontifical Academy for Life, 2005).
Cell culture is the process by which cells derived from living organisms are grown and reproduced in a controlled laboratory environment. Cultures containing animal cell-lines are used for growing viruses for use in the 5-in-1 vaccines, Pre-school and Teenage boosters, MMR vaccines, Nasal flu vaccine and Rotavirus vaccine. The polio virus element of the 5-in-1 vaccine is grown on Vero cells, that is a cell-line originally derived from the kidney of the African green monkey. The measles and mumps elements of the MMR are grown on a culture derived from cells taken from a chick embryo. These facts are sometimes distorted by anti-vaccine campaigners, in order to suggest that vaccines are a kind of witch’s potion, or that there is a risk that animal disease may be transmitted by vaccines.
An article from 2003 giving further detailed information on vaccine ingredients can be found here.
Published by Owain John
Medical content reviewed by Professor Andrew Pollard
Please email us with comments and queries, but please note that we cannot give individual advice on vaccines for you or your child. You should consult your GP or other healthcare provider if you need specific advice.
Last updated 05/03/2013