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How do vaccines work?

One of the hot questions of the moment is ‘how do vaccines work?’ We take a look at exactly what vaccines are, how they’re made, and how safe they are.

How Do Vaccines Work

It’s hardly surprising that the news has been full of talk about coronavirus vaccines lately. They are the light at the end of the tunnel for the COVID-19 pandemic. But what exactly are they? And how do vaccines work? We take a closer look at these key questions and more. 

As well as exploring the history, benefits, and safety of vaccines, we also examine how they’re developed. If you’re curious about learning more about vaccines, we’ve highlighted relevant courses that can help you further your understanding. 

What is a vaccine?

Before we get into more detail about how vaccines work, let’s start by looking at some of the basics, beginning with a simple definition of vaccines. 

A vaccine is a type of medical treatment that’s designed to prevent diseases. It does this by teaching the body’s immune system to fight off a virus or bacteria it hasn’t come into contact with before. 

Of course, that’s a very top-level explanation of what vaccines are and how they work. In reality, they’re complex pieces of scientific engineering that can take many years to develop and test. That being said, let’s look at some of the other key introductory elements. 

Vaccine meaning

The term vaccine has an interesting origin. It was first coined by British physician Edward Jenner in 1798, and it originates from the Latin vaccinus ‘from cows’ and the cowpox virus, vaccinia. Jenner noticed that milkmaids who suffered from the cowpox virus did not contract the much deadlier smallpox virus during local outbreaks.  

You might be asking ‘when were vaccines invented?’ Well, the first vaccine, made from pus taken from cowpox lesions, was administered to an 8-year-old boy in 1796. Jenner then exposed the boy to smallpox, and he did not develop the infection. 

History of vaccines 

Despite coining the term and delivering the first vaccine, Jenner’s work was by no means the first on preventing infectious diseases. There is evidence dating as far back as 1000 CE to suggest that people were using smallpox material to prevent infections in countries such as China and Turkey, as well as in some African countries.

However, it was during the 19th and 20th centuries that vaccine development really took off. As our understanding of bacteria and diseases grew, so too did our ability to combat them. 1885 saw the development of the rabies vaccine, followed by ones for diseases such as diphtheria, tetanus, cholera and tuberculosis. 

Nowadays, we have vaccines for some of the most dangerous, debilitating and deadly diseases. Depending on your stage of life, location, and travel plans, you may need different vaccines to stave off certain illnesses. 

Vaccination vs immunisation 

One term that’s often (incorrectly) used interchangeably with vaccination is immunisation. While the former refers to the process of receiving a vaccine, the latter is slightly different. Immunisation is the process by which an individual gains protection from a disease. This can be either from a vaccine or through getting and recovering from an infection

How do vaccines work? 

So, let’s get into slightly more detail – how do vaccines work? It’s a question that requires a basic understanding of how our bodies respond to certain illnesses in the first place. What’s more, as well as on an individual level, it’s important to know how vaccines work on a broader scale. 

Bear in mind that a lot of the information we cover here provides a simple introduction to vaccines. For a more detailed look, we have a variety of relevant courses available, outlined throughout. 

The body’s immune response

The human body has evolved to have several defence systems. These defences are a response to the many trillions of disease-causing organisms that surround us, such as bacteria, viruses, and other pathogens. As well things like your skin and mucus, your immune system protects you from these pathogens. 

The immune system consists of many different cells, tissues, and organs working together. When a virus or bacteria invades your body causing disease, your immune response is triggered, identifying and destroying the infectious agents. Part of this process is where your white blood cells create proteins known as antibodies. 

These antibodies track down the bacteria or virus and mark it to be destroyed. Antibodies are produced to deal with specific threats, meaning it can take time for your defences to start fighting back. In the meantime, the disease attacks your body. 

Once the bacteria or virus is dealt with and you recover, antibodies remain in the blood. What’s more, your body might produce ‘memory cells’. These cells stay in your body for years, meaning that if you encounter the same virus or bacteria again, your body’s immune response is much faster and more targeted. 

With these memory cells in place, it means that many diseases and infections you beat once often won’t make you sick again. This mechanism is also the basis of how vaccines work. 


So, we know the basics of how the body responds to viruses and bacteria. We also know that vaccines teach the immune system to fight off a disease it hasn’t come into contact with before. But how does it do that? 

Most vaccines contain a harmless form of a bacteria or virus. The original pathogen may have been weakened, killed, or broken apart before being administered. This form of the bacteria or virus is enough to trigger the body’s natural immune response, without actually causing a full-blown illness. 

Once the vaccine has been administered, and your immune system has responded, you will have the antibodies and memory cells specific to that disease. So, if you do reencounter the virus or bacteria, your body will remember it, and deal with it before you notice it’s there. 

Herd immunity

Although vaccines are the safe choice for many people, some may not be able to be vaccinated. One of the ways we can protect those who can’t receive a vaccine is through what’s known as herd immunity. 

It’s one of the buzz words you may have seen in relation to managing the COVID-19 pandemic, but what is herd immunity?  Well, it’s essentially the indirect protection from infectious diseases that comes when enough people have immunity to them, often through vaccinations. 

For those who cannot be vaccinated, herd immunity is the only thing that can protect them from the virus or bacteria. When enough people are immune, the disease cannot spread in the community, as the lines of transmission are cut off. 

The exact percentage of people who need immunity before herd immunity is achieved differs with each disease. We know that with measles, for example, around 95% of the population needs vaccinating, while for polio, it’s about 80%. According to the World Health Organisation, we don’t currently know what the figure is for herd immunity to COVID-19. 

However, if you do get vaccinated against a disease, you’re protecting yourself and other, often vulnerable people.  

Types of vaccine

There are several different types of vaccine used in modern medicine. These variations are designed to train your immune system to fight different diseases. Some of the commonly used types of vaccine include: 

  • Live-attenuated vaccines. These live vaccines contain a weakened version of the bacteria or virus to create an immune response. 
  • Inactivated vaccines. This type uses a version of the pathogen that has been killed or altered to not replicate.
  • Subunit, recombinant, polysaccharide, and conjugate vaccines. Many vaccines use only specific parts (antigens) from the surface of the bacteria or virus. 
  • Toxoid vaccines. Some bacteria release toxins when they enter the body, and some vaccines use these toxins to create immunity. 
  • Viral vectored vaccines. This newer technology uses a genetically modified form of the virus to help the body produce antibodies. 
  • mRNA vaccines. Again, this is a newer form of vaccine that uses messenger RNA, part of the virus’s genetic code, to train the body’s response. 

The last two on this list are particularly important, as the current COVID-19 vaccines use this innovative technology.  The Oxford-AstraZeneca COVID vaccine uses the viral vector method, while the Moderna and Pfizer-BioNTech vaccines use mRNA. 

The benefits of vaccines 

As you might expect given the long history of vaccinations, there have been many studies into the benefits and side effects of vaccines. Ultimately, it’s safe to say that the benefits far outweigh the potential downsides (we’ll get to those further down). 

So why are vaccines important? Below, we’ve picked out some of the benefits of vaccines highlighted by countless studies and research.

They keep you safe

By receiving a vaccine, you gain protection from diseases that can make you seriously ill or even prove fatal. Childhood vaccinations can prevent diseases such as measles and polio, for example. Similarly, if you’re travelling around the world, you can gain immunity from a host of dangerous illnesses through vaccines. The WHO estimates that vaccines prevent 2-3 million deaths per year. 

They keep others safe

When enough people in the community are vaccinated, you’re helping to prevent potentially deadly diseases from spreading to those who cannot have vaccines. This herd immunity helps to keep vulnerable people safe. 

They can eradicate diseases

Smallpox is the ultimate example of the success of vaccination programmes. The disease is thought to have originated over 2,000 years ago and was often fatal. An average of 3 in every 10 people who got the disease died, while survivors often had severe scarring. However, through vaccination, this deadly disease has been totally eradicated, and no one has naturally acquired it since 1977. 

They help society 

As well as reducing and eliminating diseases in communities, vaccines can also help to prevent related diseases. What’s more, immunisation programmes can ease the strain on healthcare systems, helping to save lives and money. Vaccines can help extend life expectancies, prevent antimicrobial resistance, and mean we can travel safely. 

How are vaccines made? 

Now that we know how vaccines work, let’s turn our attention to the process of actually making them. There are two main aspects to consider here. The first is how vaccines are developed, and the second is how they’re manufactured.  

How long do vaccines take to develop? 

The first thing to consider is the research and testing that goes into creating a vaccine. There are several stages to this process. We’ve highlighted the main steps needed, as well as how long it takes to develop a vaccine: 

  • Discovery research. This usually takes 2-5 years and involves lab research to identify potential antigens that can prevent or treat a particular disease. 
  • Pre-clinical. It can take up to two years to assess the safety and suitability of a potential vaccine. Often, this involves studies on cell cultures and animal testing. 
  • Phase I. This first phase takes 1-2 years and assesses the safety of the vaccine. It usually involves a small group of adults.
  • Phase II. This stage can take 2-3 years and examines whether or not the vaccine safely produces a sufficient immune response. 
  • Phase III. The final testing stage is a larger-scale analysis that can take 2-4 years to complete. It looks at the efficacy of the vaccine in preventing disease and infection. 
  • Regulatory approval. Regulators must approve a vaccine for use based on the research and clinical trial data. This can take 1-2 years. 

How was a COVID-19 vaccine developed so fast?

As you can see, it can often take around ten years to fully create and deploy a vaccine. So how did we develop a coronavirus vaccine in less than a year? Well, the unprecedented progress is a testament to incredible efforts of experts around the world. 

The story of the Oxford vaccine actually goes back further than the initial COVID-19 outbreak. Work started on developing a vaccine several years ago. After the deadly Ebola outbreak in 2014, scientists at Oxford University wanted to have a mechanism in place to tackle future, unknown infections. 

They developed a fast and flexible vaccine that can be altered to address specific threats. Once they had the genetic code of the coronavirus, they were able to start work making and testing the COVID-19 vaccine. Given the urgency of the project, there wasn’t the usual waiting around for funding and approval that most vaccines face. 

If you’re looking to find out more about the Oxford-AstraZeneca vaccine development process, we have a course that features input from some of the experts involved with the development process. Vaccine Development: Finding a Vaccine for COVID-19 and Future Pandemics looks at vaccine development in general, as well as the different COVID-19 vaccine candidates. 

Are vaccines safe? 

Clearly, vaccines are a vital and effective way of combating diseases. They’re also our best route out of the coronavirus pandemic. But are vaccines safe? It’s a question that, naturally, many people ask. After all, you don’t want the cure to be worse than the disease. 

The side effects of vaccines 

On the whole, the majority of people don’t suffer from any serious side effects from vaccines. That being said, there are some mild ones, including: 

  • Pain, soreness, or swelling at the injection site
  • A mild fever or chills 
  • Feeling tired and aching 
  • Headache 

These side effects are usually a sign that your body is starting to build immunity against a disease, meaning the vaccine is working. 

The rigorous testing and quality control that goes into developing vaccines means that there are very few severe side effects. There is a very small chance of a severe allergic reaction to some of the ingredients in a vaccine. However, the rate of this is around 1 in 900,000

How long do vaccines last? 

The duration of immunity tends to vary between different types of vaccines and the diseases they treat. Some, such as the measles vaccine, can offer life-long protection. Others, such as the influenza vaccine, only last around six months, because the virus is constantly evolving. 

When it comes to the COVID-19 vaccines, we don’t currently have enough data to know how long they’ll offer protection for. 

Do vaccines cause autism?

This question is asked quite frequently and seems to have worked its way into the public mind. This links back to a paper published in the late 90s that claimed to find a link between vaccines and autism. However, the subject has been closely studied in the years since, and no researchers have found a connection between the two. The vast majority of scientific and medical experts agree there isn’t one.   

What are vaccines made of?

As well as the main ingredient of a vaccine, such as a weakened or destroyed version of a bacteria or virus, there are other elements. These are usually included to make the vaccine safer and more effective. People sometimes have concerns about mercury in vaccines. However, thimerosal, as it’s known, is no longer found in most vaccines, and there is no evidence to suggest it causes harm. 

Final thoughts 

So, we’ve hopefully answered the ‘how do vaccines work’ question with enough detail to get you started. Clearly, this is a fascinating and valuable area of science that has saved the lives of millions of people. The work on the COVID-19 vaccines has been particularly amazing, and we owe a great deal to the experts who have made it possible. 

If you want to learn more about how vaccines work, we have a wide variety of relevant courses available to help. Whether you’re looking to improve your understanding or start developing your career in this interesting field, you’ll find a variety of vaccine courses to help you on your way.

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