What is a vaccine?

A weakened form of a disease-causing germ which trains your immune system to create antibodies, without causing the disease itself. When faced with this germ in the future through natural exposure, your body remembers it and quickly mounts a response – either avoiding illness entirely or reducing severity and/or length of symptoms.

They were first invented in 1796 by English physician Edward Jenner. He is credited with creating the first vaccine by using cowpox matter to protect against the much more dangerous disease smallpox. Less well known, is that 22 years earlier a farmer called Benjamin Jesty formed and tested the exact same idea and it’s likely that Jenner got to hear of Jesty’s work. Reflecting how the first vaccines were developed, the word "vaccine" comes from the Latin word for cow, “vacca”.

Why is vaccination important?

Vaccination is one of the most important steps we can take to protect our health and the health of our children. Vaccinations prevent millions of deaths worldwide every year.

Since vaccines were introduced in the UK, devastating diseases like smallpox, polio and tetanus that used to kill or disable millions of people have either disappeared or are now extremely rare. Other diseases have reduced to a very low numbers since vaccines were introduced and these cases are often related to travel abroad.

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

Vaccine safety

For all the vaccines used in the current UK routine schedule, the overwhelming evidence is that vaccinating is safer than not vaccinating.

Vaccines go through many stages of development, testing for effectiveness and serious side effects, before being offered to the public. They are then constantly monitored for rare side effects and to ensure they are still effective.

Vaccines sometimes cause mild side effects that will not last long – you may feel a bit unwell and have a sore arm for 2 or 3 days. 

As with any medicine or food, there is a very small chance of a severe allergic reaction (anaphylaxis). Anaphylaxis is extremely serious but can be treated with adrenaline. Healthcare workers who give vaccines know how to deal with this. In the UK between 1997 and 2003 there were a total of 130 reports of anaphylaxis following ALL immunisations. During these six years, around 117 million doses of vaccines were given in the UK. This means that the overall rate of anaphylaxis is around 1 in 900,000.

Deciding whether to have a vaccine

Always use reputable and trusted sources to get information on vaccinations, such as NHS doctors and nurses, Health Protection staff, School Aged Immunisation Service staff and their websites, leaflets and posters. There is a lot of incorrect information on vaccines on social media which could put you or your child at risk.

Deciding whether or not to you or your child have a vaccine is about weighing the risks of having the vaccine against the risks of not having it, which involves assessing the risks of catching the disease and the likely severity of illness.

For some of the information, it can be quite easy to find out, and some comparisons are quite easy to make. For example, we know that 1 in 5000 children develop encephalitis as a complication of measles, but less than 1 in a million develop encephalitis as a complication of the MMR vaccine.

Unfortunately, the chance of getting a disease is difficult to work out, because it depends on lots of factors such whether the disease spreads to your area, levels of vaccination coverage in your area and how it’s dealt with. If lots of people around you are unvaccinated, there is more chance of diseases spreading quickly and this increases the risks. 

It can therefore be difficult to weigh up the risks and decide what is best for you or your child. The outcome of this can be that you do nothing. Although doing nothing can make people feel less guilty if something goes wrong, because they can tell themselves that it’s just bad luck, they haven’t “done nothing” – they’ve actually made a decision which may have consequences and could lead to similar or worse levels of guilt, if, for example, their child suffers severe complication from catching a vaccine-preventable disease.

Checking vaccination status for you or your child

You can check your child’s “Red Book”, check the NHS App: https://www.nhs.uk/nhs-app/help/health-records-in-the-nhs-app/gp-health-record/ or contact your GP.

Vaccine characteristics

Vaccines are more effective than almost any other medicine we use on a daily basis.

Some vaccines in the routine UK schedule are almost 100% effective against some diseases. For example, after two doses of MMR vaccine up to 99% of individuals will be protected from catching measles.

Some vaccines work less well with older people, as their immune system tends to be less effective.

When looking at how effective vaccines are, it’s important to distinguish between protection from catching the disease and protection from severe illness. Some vaccines are really good at preventing infection in the first place, while others are less good at that but do provide good protection from severe illness, so are still worth having.

Because some viruses change very rapidly, the vaccination needs to be changed and given again, for example the flu vaccination needs to be re-formulated every year based on the strains circulating at the time, and its effectiveness can vary from year to year.

In contrast, the measles virus hardly changes from year to year, and so the measles vaccine that forms part of the MMR/MMRV is as likely to protect you today as it was ten years ago.

Vaccines are developed to protect against the main types that cause disease, and different vaccines may be needed for different types. For example, the MenACWY vaccine protects against the A, C, W and Y types of the Neisseria meningitidis bacteria which causes meningitis, but not the B type. A different vaccination is required for this.

Sometimes new strains appear, or less common strains start to cause more disease. This can also have an impact on vaccine effectiveness.

Most vaccines offer good protection for many years, but for some vaccines it is necessary to give repeated doses or boosters to provide continued protection. Vaccines do not usually provide protection forever.

Levels of protection may also be reduced because of medical conditions, medications or ageing, when the immune system may work less well.

Herd immunity

When a high percentage of the population is vaccinated, it is difficult for infectious diseases to spread because there are not many people who can be infected.

For example, if someone with measles is surrounded by people who are vaccinated against measles, the disease cannot easily be passed on, and it will quickly disappear again.

This gives protection to vulnerable people such as new-born babies, elderly people and those who are too sick to be vaccinated.

It doesn’t work where diseases are caught directly from the environment e.g. tetanus

Types of vaccine

Although all vaccines work on the same basic principle, there are various types.

Whole pathogen vaccines:

  • The oldest method uses the whole pathogen in a vaccine to produce an immune response like seen during natural infection. This can cause active disease and can be dangerous to the individual receiving it and risks disease spread. To avoid this, modern vaccines use pathogens that have been altered.
  • Live attenuated vaccines contain whole germs which have been “weakened” (attenuated) so that they create an immune response but don’t cause disease in healthy people.
  • Inactivated vaccines contain whole bacteria or viruses which have been killed or have been altered, so that they cannot replicate. Because inactivated vaccines do not contain any live bacteria or viruses, they cannot cause the diseases against which they protect, even in people with severely weakened immune systems.

Sub-unit vaccines:

  • These vaccines typically contain one or more specific antigens from the surface of the pathogen. An antigen is a specific molecule, usually on the surface of a cell or pathogen like a virus or bacterium, that triggers an immune response in the body.
  • They do not always create such a strong or long-lasting immune response as live attenuated vaccines. They usually require repeated doses initially and subsequent booster doses in subsequent years.

Nucleic acid vaccines:

  • They provide the genetic instructions of the antigen to cells in the body and in turn the cells produce the antigen, which stimulates an immune response. They are quick and easy to develop and provide significant promise for the rapid development of vaccines in the future.
  • These include mRNA vaccines, such as the Pfizer and Moderna COVID vaccines. 
  • They use messenger RNA inside a fat membrane. This fatty cover both protects the mRNA when it first enters the body and helps it to get inside cells by joining with the cell membrane. Once the mRNA is inside the cell, machinery inside the cell translates it into the antigen protein. This mRNA typically lasts a few days, but in that time sufficient antigen is made to stimulate an immune response. It is then naturally broken down and removed by the body. RNA vaccines cannot combine with the human genetic code (DNA).

Viral vectored vaccines:

  • These use a modified harmless virus to carry the vaccine into the body.
  • The Oxford Astra-Zeneca COVID vaccine is an example of this.

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