How are vaccines made?

Not all vaccines are made in the same way. Vaccines can be made using:

  • viruses or bacteria that have been killed (killed vaccines)
  • weakened (or attenuated) viruses or bacteria that can multiply in the body but do not cause disease in healthy people (live vaccines)
  • bacterial toxins that have been altered and inactivated (toxoid vaccines) so that they no longer cause disease
  • small parts of the bacteria or virus (subunit vaccines)
  • parts of the bacterial polysaccharide (a type of sugar) coating or capsule that surrounds the bacteria; these are polysaccharide vaccines
  • pieces of the bacterial polysaccharide capsule can be chemically attached to a harmless piece of protein to stimulate the immune system and trick it into remembering the pieces of capsule; these are called conjugate vaccines
  • more than one type of virus and/or parts of bacteria (combination vaccines).

Other ingredients

Vaccines also contain other ingredients that are included in the vaccine for a specific reason, such as preservatives (e.g. minute amounts of an antibiotic) to make sure the vaccine does not become contaminated.

For more in-depth information, read about other vaccine ingredients and see our FAQs.

Killed vaccines

Killed vaccines, as the name suggests, contain viruses or bacteria that have been killed and cannot cause disease. However, they are still intact and can be seen or recognised by your immune system. The vaccine will stimulate an immune response to the virus or bacteria that will protect you from future infection.

The polio and hepatitis A vaccines are killed vaccines.

Live vaccines

Live vaccines contain weakened versions (attenuated strains) of the virus or bacteria, which won’t cause disease but can multiply inside your body to help your immune system develop an immune response.

The measles, mumps and rubella (MMR), chickenpox (varicella zoster), yellow fever, shingles (herpes zoster), tuberculosis (TB) or Bacillus Calmette-Guérin (BCG) vaccine and the typhoid vaccines are all live (or attenuated) vaccines.

Live vaccines are not recommended for pregnant women or anyone who is at high risk of infection due to a weakened immune system. This includes people:

  • who are HIV positive
  • who have had a bone marrow or organ transplant
  • with cancer
  • taking medicines that suppress their immune system.

Toxoid vaccines

Some bacteria cause disease by producing toxins. These toxins can be collected and made harmless (inactivated) and used to make a vaccine. The inactivated toxins (i.e. toxin-like or toxoids) in the vaccine are not poisonous or toxic to the body, but they can stimulate the body’s immune response to protect you from the toxin produced by the bacteria in the future.

The tetanus and diphtheria vaccines are toxoid vaccines.

Subunit vaccines

These vaccines only contain pieces (or subunits) of a virus or bacteria — the parts of the virus or bacteria that would be recognised by your immune system if you were naturally infected with the whole organism. Subunit vaccines allow your body’s immune system to recognise these parts and will protect you from a future infection.

These vaccines are less likely to cause side effects (e.g. fever and soreness at the injection site) compared with vaccines that contain killed or live attenuated viruses.

The hepatitis B, Haemophilus influenzae type b (Hib), and human papillomavirus (HPV) vaccines are all subunit vaccines.

Polysaccharide vaccines

Many bacteria have a polysaccharide (a type of sugar) coat that surrounds them. Polysaccharide vaccines contain parts of this polysaccharide coat, which can stimulate an immune response.

Some bacteria (e.g. the bacteria that cause pneumococcal disease) can have many closely related strains (called serogroups or serotypes). Each serotype has a different type of polysaccharide coat. Vaccines against these bacteria contain a mixture of these different types of polysaccharides, to stimulate immunity to all the serotypes. For example, the pneumococcal vaccine Pneumovax 23 contains 23 different types of polysaccharides to protect you against all the 23 serotypes that commonly cause pneumococcal disease.

The antibodies that your body makes against these polysaccharide vaccines do not last very long, so you may need to have another vaccination in 3–5 years’ time. Polysaccharide vaccines do not work well in children younger than 2 years old because their immune systems are still developing and don’t yet recognise vaccines that only have polysaccharides in them.

The pneumococcal, typhoid and some meningococcal vaccines are polysaccharide vaccines.

Conjugate vaccines

Many bacteria have a polysaccharide (a type of sugar) coat that surrounds them. Conjugate vaccines contain parts of this polysaccharide coat, chemically attached to a harmless protein that "carries" it. This increases the chances that the immune system will respond to the pieces of polysaccharide coat. It also means that the immune system of children younger than 2 years old can respond well to these types of vaccines.

The Haemophilus influenzae type b (Hib) vaccine and the pneumococcal vaccines (Synflorix or Prevenar 13) are conjugate vaccines.

Combination vaccines

Combination vaccines contain several different types of killed or live viruses and bacteria or toxoids that cause various diseases. A single injection of a combined vaccine will protect you against all the diseases caused by the organisms contained in the vaccine. For example, there is a combination vaccine that protects you from diphtheria, tetanus, whooping cough (pertussis), hepatitis B, polio and Haemophilus influenzae type b (Hib).