How do Vaccinations Work?

A critical part of health services across the world, vaccines are an invaluable resource that protect countless people of all ages from serious illness every year. Vaccinations have become an integral part of our society, and in doing so they have massively reduced the incidence of otherwise highly contagious and virulent conditions like measles, diphtheria, and polio. Through vaccination these and many other illnesses have gone from being widespread infections to extremely rare cases. In this article we look at how exactly vaccines achieve this end.

The Immune System

Your body is equipped with its own fantastic defence system, designed to protect you from the countless infectious agents you meet every day. This mechanism is called the immune system, and is a complex network of different kinds of cells and molecules that work together to combat the effects of bacteria and viruses.

Different infections have different modes of action, and the multitude of bacteria and viruses in existence are virtually all unique in some way. This means that your body needs to be able to defend against all of these individual agents, and it does so by remembering the characteristics of viruses and bacteria it is exposed to.

Once infected, your body begins an immune response against the agents responsible. This response is quite complicated, and an important part of it is the generation of memory cells and antibodies specific to the invading virus or bacteria. Once an infection has passed the immune response fades away, but some memory cells linger, ready to react quickly if the infection recurs. After an initial exposure, the body becomes primed against the infection and is able to deal with it quickly and without a serious illness developing, and this is what vaccination aims to exploit.

The mechanism of vaccine action

There are in fact a number of different types of vaccine, and these have unique modes of action but share a single principle: they work by effectively priming your immune system against a particular infection. A vaccine acts as an initial exposure to a particular disease causing pathogen, but without the risk of serious illness that natural exposure to that particular pathogen would carry with it.  

Conditions like measles, meningitis C, and diphtheria cause severe symptoms and illness if your body has not been previously exposed to them. These diseases are also highly contagious and therefore pose a serious risk not only to individuals, but to whole communities. This is an important part of the use of vaccines, the fact that they confer their protection to whole groups by limiting the spread of virulent agents.

Vaccination programmes

Vaccines are sometimes provided as one off doses that are enough to provide a person with immunity against a condition. However other vaccinations require several doses over a period of time before they confer sufficient protection. In the UK the NHS provides vaccinations through a programme or immunisation timetable which aims to ensure that every one of a particular age within a certain population is provided with a vaccination. These programmes are an important part of how vaccines work as they are devised to stimulate the immune system to the point where it can handle any exposure to a disease on its own.

As a vaccination programme is implemented the incidences of infection begin to drop, and once enough people have gained the protection vaccines have to offer, the whole population begins to reap the benefits as transmission of the disease causing virus or bacteria is massively reduced. At this point a population begins to demonstrate herd immunity, which means that disease is more difficult to transfer between people who are vaccinated and those who are not.

Herd immunity is an important mechanism by which people who can’t have a vaccination can gain some measure of protection against dangerous pathogens. People who are immunocompromised (have weakened natural defences) or are receiving chemotherapy for cancer can’t safely receive vaccination, and so greatly benefit from herd immunity.

This article has briefly outlined how vaccinations work, and while there are a variety of different vaccines that all take different approaches towards promoting immunity against disease, the general principles apply to all of them.

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