Live Vaccine

Vaccination is an important part of modern medicine as it protects people from diseases and infections which could potentially pose a serious health risk. Their usefulness is such that vaccines are used across the world and recognised for their effectiveness in bolstering our natural immunity.

Because of the immense variation in disease causing organisms like virus and bacteria, there is a need for a variety of different vaccination methods to safely provide prophylaxis (protection against a future infection) to men and women of all ages and walks of life. One particular form of vaccine is referred to as a ‘live’ vaccine, or sometimes as an attenuated vaccine. In this article we look at what a live vaccination actually is and how it differs from other types of immunisations. 

What is a live or attenuated vaccination?

Live or attenuated vaccines are formulated with a living version of the pathogen (disease causing microbe) responsible for a particular condition. This type of vaccine is also referred to as attenuated because it is often treated in such a way that the microbe is not as potent as it would normally be. This makes it a safer, weaker version of the disease to which your body can respond by preparing an appropriate immune response. Because of this exposure, any future infection to this illness will be quite mild as your body is prepared to defend against it.

Why use live vaccines?

You may be wondering why a live version of a microbe, albeit a weakened or attenuated one, would be used for immunisation where alternatives are available. In reality a live vaccine is actually an excellent way of effectively ‘training’ the immune system to deal with infections. This is because this type of vaccine is as close to the real pathogen as you can get without actually triggering the illness, and as such provide an excellent method of immunisation.

What are live vaccines used for?

Live/attenuated vaccinations are used for a range of different conditions including measles, chickenpox, and mumps. These are all viral infections, and viruses are simple microbes that are easy to attenuate to form live vaccines.

A virus is little more than a small amount of genetic material coated in protein, and so their properties and behaviours can be readily controlled by scientists. The majority of live, attenuated vaccines are derived from and for viruses.

Pros and cons of live vaccines

The advantages of live vaccines were touched on briefly earlier in his article, and are basically the ease with which this type of immunisation can be prepared for viral infections and their effectiveness in preparing the immune system for an infection. Live viruses induce a strong immune response which means that you receive longer lasting immunity from a small number of doses.

There are, however, some limitations to the uses of live vaccines. With a few exceptions like yellow fever bacteria, live vaccines can only really be prepared for viral infections, meaning that a host of bacteria would have to be vaccinated against by other means.

Live vaccines also need to be carefully refrigerated otherwise they lose their effectiveness. This can be an issue as many of these agents are prepared overseas and need to be shipped long distances to where they are needed. Moreover some countries desperately in need of vaccinations can sometimes struggle to provide adequate storage conditions.

A live vaccine, while highly effective in inducing an immune response, can pose a more serious risk to people with immune systems that don’t work very effectively. A person with a weakened immune system is referred to as immunocompromised, and if a person is compromised in this way (usually because of an immune disease like HIV or chemotherapy) live vaccines can be potentially dangerous.

Finally a major concern when using live vaccines is the possibility that the prepared agents revert to a virulent form of the disease. The genetic material of all living things is subject to changes called mutations, and where simple organisms like viruses are concerned, a small mutation can have major consequences. Some mutations can restore virulence (infectious ability) to an attenuated vaccine, and while the chances of this are very small, it is something that has happened in the past and can be a serious concern.

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