Conjugate Vaccine

Conjugate vaccines are one of a number of different approaches to immunisation currently in use to protect against infectious diseases. In this article we look at what these vaccines do and how they work, as well as how they are currently being used.

What are conjugate vaccines?

Unlike some other types of vaccination, conjugate vaccines are made up of whole pathogens, but are instead composed of elements of bacteria chosen for their immunogenic ability. An ‘immunogen’ is a molecule or compound that is a part of a pathogen to which our immune system responds. Immunogens are so called because they can be used to immunise individuals to a disease without the need for direct exposure to the causative pathogen.

The immunogen within conjugate vaccines has two parts. The first is a surface marker called an antigen taken from bacteria with a characteristic sugar (polysaccharide) coating. This coating is highly specific to particular bacteria, and can be used to ‘teach’ the immune system how to deal with the associated bacteria quickly and efficiently. Unfortunately on its own a polysaccharide antigen does not make an effective immunogen, which is why it is coupled to a carrier protein, forming a structure which our body identifies as an invader and promptly targets and removes.

Conjugate vaccines are effective against bacteria possessing a distinctive polysaccharide coat, particularly as younger children with immature immune systems can be vulnerable these types of bacteria. The coating can disguise antigens, allowing the bacteria to evade an immune response and pose a threat to the health of infected children.

What are conjugate vaccines used for?

Conjugate vaccines are currently used to immunise against virulent diseases like Haemophilus influenzae B (Hib) and pneumococcus. These are good examples as injections immunising against these diseases are an important part of the UK’s childhood immunisation programme. Hib and pneumococcus can cause a number of dangerous diseases including infections like meningitis and pneumonia.

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