Vaccines

Understanding vaccines

A vaccine is a medicine to protect against a specific disease.

Vaccines are mainly given through an injection but can also be given orally (by mouth) or sprayed into the nose. 

Uses of vaccines

Vaccines are a simple and effective way to help protect you against harmful diseases caused by bacteria or viruses such as flu, measles, and COVID-19.

What is in vaccines

Vaccines contain a safe version or small part of a virus, bacteria, or toxin that’s been weakened or destroyed.

Some vaccines contain substances called adjuvants that boost the body’s immune response to the vaccine. These ingredients may include:

• aluminium
• squalene oil
• pork gelatine
• egg protein
• formaldehyde
• antibiotics

These ingredients make the vaccine safer and more effective. They are not harmful in the small quantities used in vaccines.

There is no evidence to suggest any increased risk for neurodevelopmental disorders including autism, with early childhood exposure to vaccines with aluminium.

Find out more about vaccine ingredients at:

• Electronic medicines compendium

Types of vaccines

Your immune system is your body’s natural defence system that helps to fight off infections and diseases.

An immune response is the way the body defends itself against substances it sees as harmful or foreign.

How your body reacts to a vaccine depends on what type of vaccine it is.

Inactivated vaccines

Inactivated vaccines contain viruses or bacteria that have been killed and cannot cause disease.  

Live-attenuated vaccines 

Live-attenuated vaccines contain a weakened form of the virus or bacteria that cannot cause serious disease.   

Subunit, recombinant, or conjugate vaccines 

Subunit, recombinant, or conjugate vaccines contain only small parts of the virus or bacteria, such as proteins that trigger an immune response.

Toxoid vaccines 

Toxoid vaccines contain inactivated toxins that are produced by a microorganism that causes a disease such as viruses, bacteria, fungi or protists. This is called a pathogen. 

These vaccines are important as some diseases are caused by the toxins the pathogen produces, and not the pathogen itself. 

Viral vector vaccines 

Viral vector vaccines contain a modified, harmless virus (called a vector) that delivers genetic instructions to your cells to make proteins, triggering an immune response. 

Messenger RNA (mRNA) vaccines 

Messenger RNA (mRNA) vaccines contain a piece of mRNA that give your cells instructions on how to make a small, harmless part of a protein found in a virus or bacteria.

Your immune system recognises these proteins and produces antibodies to fight them off.   

How vaccines work

Vaccines train your immune system to recognise specific infections.

When a vaccine is given, a small, harmless part of the virus, bacteria, or toxin is introduced into the body.

Vaccines teach your immune system how to recognise the infection and create protective proteins, called antibodies to fight off the infection in the future.

This can protect against diseases altogether or make their symptoms much milder.

It's much safer for your immune system to learn this through vaccination than by catching the diseases and treating them.

Once a vaccine has taught your immune system how to fight a disease, it can often protect you for many years.

Why vaccines are important

Vaccines are proven to protect you against serious illnesses.

Getting vaccinated is one of the most effective ways to protect yourself and others from harmful diseases. 

They prevent up to three million deaths worldwide every year.

Vaccines help to prevent the spread of harmful bacteria and viruses which can make you seriously unwell.

By making sure your own vaccinations are up-to-date, you can help protect yourself and your loved ones who may be vulnerable to infectious diseases.

Having a vaccine also benefits your whole community through "herd immunity".

If enough people are vaccinated, it's harder for the disease to spread to those people who cannot have vaccines, such as, people who are ill or have a weakened immune system.

Since vaccines were introduced in the UK, diseases like smallpox, polio and tetanus that used to kill or disable millions of people are either gone or seen very rarely.

Other diseases like measles and diphtheria have been reduced by up to 99.9 per cent since their vaccines were introduced.

If people stop having vaccines, it's possible for infectious diseases to quickly spread again.

How vaccines are made

Before any vaccine is made available for public use, it goes through a rigorous development process to test its safety, quality and effectiveness.

This includes laboratory research, safety testing, and clinical trials.

Vaccine clinical trials are controlled scientific studies that test for the safety and usefulness of a vaccine in protecting against diseases before it is approved for public use.

Clinical trials typically involve multiple testing phases involving people of different ages, genders and ethnic backgrounds to make sure the vaccine is safe and effective for everyone.

Vaccines are batch-tested to make sure that each batch of products meets the necessary quality standard.

All vaccines used in the UK go through robust monitoring and surveillance.

Regulatory bodies like the MHRA regularly track and review adverse drug reaction reports through the Yellow Card scheme to make sure vaccines stay safe.

Vaccine side effects

As with every medicine, it is important to familiarise yourself with the information in the product information sheet.

Vaccination symptoms are normally mild and last less than a week.

Any medicine, including vaccines, can cause an unwanted side effect.

Some very common side effects of vaccination include:

• general aches, or mild flu-like symptoms
• pain and tenderness in the arm where you had your injection which could last for two to three days
• headaches
• feeling tired
• babies or young children feeling a bit unwell or developing a high temperature for one or two days

Some children might also cry and be upset immediately after the injection. This is a normal response.

Vaccines are regularly assessed to make sure the benefits of the vaccine in preventing disease far outweigh the risks of known side effects in patients who receive them.

Allergic reactions

It's rare for anyone to have a serious allergic reaction to a vaccination. If this does happen, it usually happens within minutes.

The person who vaccinates you or your child will be trained to recognise allergic reactions and treat them immediately. With quick treatment, you or your child will make a good recovery.

Report side effects to the Yellow Card scheme

You should report any suspected side effects of vaccination to the MHRA  using:

• the Yellow Card website
• the Yellow Card app - download from the Apple App Store  or  Google Play Store 

Reports give the MHRA a better understanding of vaccine experiences and identify issues as early as possible to keep everyone safe.

Vaccines are one of the safest and most effective ways to protect yourself and others from harmful diseases. 

Vaccines are rigorously tested before being approved for use and are continuously monitored for safety and effectiveness.

By getting vaccinated, you help to reduce the spread of infections and protect yourself and others from serious diseases.

Vaccine myths

There is misleading information about vaccines online.

When making the decision to receive a vaccine or to have your child vaccinated, it’s important to know that vaccines:

• do not cause autism – there is no evidence of a link between the MMR vaccine and autism
• do not overload or weaken the immune system – it is safe to give children several vaccines at a time and this reduces the number of injections they need
• do not cause allergies
• do not contain mercury
• do not contain ingredients which cause harm in such small amounts – however speak to your doctor if you have any concerns about ingredients such as egg protein or gelatine