Types of vaccine

Vaccines can be divided into two main types.

1. Live attenuated vaccines

Live attenuated vaccines contain whole bacteria or viruses which have been “weakened” so that they create a protective immune response but do not cause disease in healthy people.

Live vaccines tend to create a strong and lasting immune response and are some of our best vaccines. However, live vaccines are not suitable for people whose immune system does not work, either due to drug treatment or underlying illness. This is because the weakened viruses or bacteria can multiply too much and might cause disease in these people.

Live attenuated vaccines used in the UK schedule:

Live travel vaccines used in the UK:

  • Yellow fever vaccine
  • Oral typhoid vaccine (not the injected vaccine)

2. Inactivated vaccines

Inactivated vaccines contain whole bacteria or viruses which have been killed, or small parts of bacteria or viruses, such as proteins or sugars, which cannot cause disease. There are several different types of inactivated vaccine which are explained below.

Because inactivated vaccines do not contain any live bacteria or viruses, they cannot cause the diseases against which they protect, even in people with severely weakened immune systems. However, inactivated vaccines do not always create such a strong or long-lasting immune response as live vaccines. They usually require repeated doses and/or booster doses. Adjuvants such as aluminium salts are often added to inactivated vaccines. These are substances which help to strengthen and lengthen the immune response to the vaccine. As a result, common local reactions (such as a sore arm) may be more noticeable and frequent with inactivated vaccines.

A. ‘Whole killed’ vaccines

These vaccines contain whole killed viruses. (There are currently no vaccines used in the UK which contain whole killed bacteria. Before 2004, the whooping cough vaccine contained whole killed pertussis (whooping cough) bacteria, but it has now been replaced with another type.)

‘Whole killed’ vaccines used in the UK schedule:

Examples of ‘whole killed’ travel vaccines used in the UK:

  • Rabies vaccine
  • Japanese encephalitis vaccine

B. Subunit vaccines (sometimes called ‘acellular’)

Most of the vaccines in the UK schedule are subunit vaccines which do not contain any whole bacteria or viruses at all. (‘Acellular’ means ‘not containing any whole cells’.) Instead these kind of vaccines contain polysaccharides (sugars) or proteins from the surface of bacteria or viruses. These polysaccharides or proteins are the parts that our immune system recognises as ‘foreign’, and they are referred to as antigens. Even though the vaccine might only contain a few out of the thousands of proteins in a bacterium, they are enough in themselves to trigger an immune response which can protect against the disease.

There are several different types of subunit vaccine which are described below.

Toxoid vaccines

Some bacteria release toxins (poisonous proteins) when they attack the body. The immune system recognises these toxins in the same way that it recognises polysaccharides or proteins on the surface of the bacteria. Some vaccines are made with inactivated versions of these toxins. They are called ‘toxoids’ because they look like toxins but are not poisonous. They trigger a strong immune response.

Toxoid vaccines used in the UK schedule:

Conjugate vaccines

‘Conjugate’ means ‘connected’ or ‘joined’. In the early days of polysaccharide vaccines (made using sugars from the surface of bacteria), it was found that they did not work well in babies and young children. Researchers discovered that they worked much better if the polysaccharide was attached (conjugated) to something else that they knew created a strong immune response. In most conjugate vaccines, the polysaccharide is attached to diphtheria or tetanus toxoid protein (see ‘Toxoid vaccines’ above). The immune system recognises these proteins very easily and this helps to generate a stronger immune response to the polysaccharide. On product information sheets the diphtheria toxoid is often called ‘CRM197 carrier protein’, because it is almost the same as diphtheria toxoid but not quite.

Conjugate vaccines used in the UK schedule:

  • Hib vaccine (in the 6-in-1 vaccine and Hib/MenC vaccine), which contains a polysaccharide joined to tetanus toxoid
  • MenC vaccine (in the Hib/MenC vaccine), which contains a polysaccharide joined to tetanus toxoid
  • PCV (children’s pneumococcal vaccine), which contains polysaccharides from the surface of 13 types of the bacteria which causes pneumococcal disease joined to diphtheria toxoid (CRM197)
  • MenACWY, which contains polysaccharides from the surface of four types of the bacteria which causes meningococcal disease joined to diphtheria or tetanus toxoid

Recombinant vaccines

Recombinant vaccines are made using bacterial or yeast cells to manufacture the vaccine. A small piece of DNA is taken from the virus or bacterium against which we want to protect. This is inserted into other cells to make them produce large quantities of active ingredient for the vaccine (usually just a single protein or sugar). For example, to make the hepatitis B vaccine, part of the DNA from the hepatitis B virus is inserted into the DNA of yeast cells. These yeast cells are then able to produce one of the surface proteins from the hepatitis B virus, and this is purified and used as the active ingredient in the vaccine.

Recombinant vaccines used in the UK schedule:

Other subunit vaccines used in the UK schedule:

Examples of subunit travel vaccines used in the UK:

  • Injected typhoid vaccine (a polysaccharide vaccine)

 

Page last updated: 
Thursday, January 3, 2019