Toxoid Vaccine

In order to effectively vaccinate against the myriad of different microorganisms causing disease, a variety of different immunisation technologies have been developed. While the first few vaccines relied exclusively on using either inactivated (killed) or weakened (live) viruses and bacteria, advances in our understanding of microorganisms and immunology have allowed for the development of a host of different approaches to vaccination. In this article we look at one of these approaches, the toxoid vaccine, and how it works.

How do toxoid vaccines work?

Different microorganisms cause harm to the body through different mechanisms and pathways. Some bacteria exert their harmful effects through the release of potent chemicals called. These toxins disrupt normal bodily functions, and are eventually responsible for disease.

When a toxin has been identified as the main means by which a bacterium causes disease, it can be used to immunise the body against that particular pathogen. Through treatment processes like chemical or heat inactivation, a toxin can be made into a harmless toxoid. Toxoids retain the same structure as their parent compound, the harmful toxin, but can no longer damage the body, therefore becoming a useful vaccination tool.

The important point to make about toxoids is that despite losing their ability to damage the body, they retain an important property called ‘immunogenicity’. This basically means that they are still recognised by the body as harmful, thereby inducing an immune response that prepares the body for future infection and exposure to the original toxin.

Part of our body’s natural defensive response to toxins is to release antibodies, highly specific immune molecules engineered by our bodies to inactivate toxins. A toxoid gets our bodies to produce these antibodies, which remain in the bloodstream, ready for future exposure to the real toxin. Moreover the vaccine teaches our immune systems how to quickly generate those antibodies should we encounter the toxin again.

How effective are toxoid vaccines?

Toxoid vaccines are extremely effective against bacteria whose harmful effects are caused by toxins. In these cases the inactivation of the toxin is enough to protect the body against infecting bacteria. In cases where bacteria are directly responsible for disease, toxoids do not confer any immunity as the vaccine does not mimic exposure to the actual bacteria.

What are examples of toxoid vaccines?

Diphtheria, botulism, and tetanus are three highly infectious diseases caused by toxin releasing bacteria. All three diseases can be vaccinated against through the use of toxoid vaccines. Tetanus is caused by the release of tetanospasmin, while botulism is caused by the release of botulin and diphtheria through diphtheria toxin.

All three compounds can be inactivated by either heat or chemical treatment, and after purification steps can be used as effective vaccines providing lasting immunity against all three diseases.

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