The use of human and animal products in vaccines

(GOV.UK) – Many pharmaceutical products and devices that are commonly used to treat illnesses, use animal-based products to perform important functions including fillers, diluents, capsules and lubricants.

As vaccines are generally complex biological products, a large number of animal-derived products are often used in their manufacture.

These products are essential to ensure the safety, potency and stability of the product and their use is highly regulated.


Vaccines are life-saving medicinal products, which are given to protect individuals against serious infections. Some vaccines contain small amounts of viruses or bacteria that have been inactivated by chemical treatment – these ‘killed’ vaccines cannot cause the disease they prevent.

Other vaccines contain micro-organisms which, although alive, are not able to cause serious disease (live attenuated vaccines). Vaccines may also be composed of purified fractions of these micro-organisms or even from selected components that are synthesised using DNA technology. All these vaccines are designed to safely protect people from potentially serious diseases.

Newer vaccines are also being used where genetic material is delivered into the host cells and the body’s own cells then generate a protein from the target organism.

There are 2 main ways in which the genetic material is delivered into the cell. One form uses a vector (a modified virus which cannot cause illness in the person vaccinated) to deliver a small amount of the pathogen’s genetic code (DNA or RNA) into a cell. The other uses a lipid (fat) envelope to deliver the genetic code.

As these vaccines do not contain the rest of the genes from the organism, they cannot cause the illness in those who are vaccinated, thus ensuring that the vaccine is very safe.

Vaccine production

Vaccines are usually made by growing cultures of the target virus or bacterium. Viruses need to grow in cells and so vaccine viruses are often grown in eggs (example influenza) or in cell lines derived from mammals, including humans.

These cell lines used to grow the virus will derive from a primary culture of cells from an organ of a single animal which has then been propagated repeatedly in the laboratory, often over many decades. For example, measles vaccine is grown in chick embryo cells and polio vaccines are grown in a mouse cell line. Another animal cell line, now being used to make egg-free flu vaccine, was derived in 1958 from the kidney of a cocker spaniel. Using these cell lines avoids any ongoing harm to animals.

The best-known human cell line is MRC5; these cells derive from the lung of a 14-week-old male fetus from a pregnancy that was terminated for medical reasons in 1966. This cell line is used to grow viruses for vaccines against rubella, chickenpox and hepatitis A.

Other fetal cell lines, collected in the 1970s and 1980s, have been used for other vaccines, including influenza and some of the new COVID-19 vaccines. No fetal material is present in the final vaccine.

The moral issues around the use of vaccines grown on fetal cell lines have been discussed within the Catholic Church. The Church notes that the cells lines are distant from the initial termination, and states that acceptance of such vaccines where there is no appropriate alternative does not signify cooperation with abortion.

Other vaccines are made in cells that have undergone genetic modification (recombination) so that they express the protein from the target organism. The cell lines used for these recombinant vaccines include yeast (hepatitis B vaccine) and insects (human papillomavirus vaccine).

Vaccines based on genetic material are an exception in that the DNA or RNA can be synthesised chemically. However, for some of these vaccines, cell lines (animal or bacterial) may be required during development and products derived from animals (such as enzymes) may be used earlier in the production process.

Animal products used to make vaccines

Bacterial cultures and viral cell lines need to be grown in special liquid called ‘culture media’, as do the bacterial, insect or mammalian cells that are used to express recombinant proteins.

This culture media provides numerous nutritious elements and growth factors that may have been obtained from materials of animal origin, such as serum, milk and milk derivatives, gelatine, meat extract or extracts from other muscular tissues.

These components are used in the early stages of the manufacturing and are not present, or may only be present in trace amounts (residues) in the final vaccines. The products used in vaccine development are all are subject to careful safety and quality checks that are scrutinised by the independent regulators.

Animal enzymes are also used during the manufacture of vaccine viruses but subsequent washing, purification and dilution steps removes them from the final vaccine. One example is trypsin, normally derived from pigs, which is widely used during the manufacture of vaccines, usually being added to the final cell culture to activate the vaccine virus.

Trypsin is also used during the manufacture of other medical products (example insulin and heparin). Although the enzyme is used as a raw material in the early steps of the vaccine manufacturing, it is then eliminated in the later steps of the manufacturing process.

Porcine trypsin in used in some injected influenza vaccines, and in vaccines against rotavirus, chickenpox and polio. It’s use, and subsequent elimination from the vaccine, has been considered acceptable by some Muslim scholars[footnote 2].

The Eastern Mediterranean Region (EMRO) of the World Health Organization (WHO) has a statement on their website about the use of porcine trypsin in oral polio vaccine (see the WHO Polio Eradication Initiative below). Although this vaccine is no longer used in the UK, similar considerations should apply to other vaccines.

Products that are used in the manufacture of a vaccine but which are not contained in the final vaccine are not generally listed on the Summary of Product Characteristics (SmPC). The SmPC is a legal document approved by the independent regulators as part of the authorisation of each vaccine.

Residues should only be included in the SmPC if they are of known clinical relevance, for example antibiotics or components that are known cause allergies.

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