VaccinationsHow vaccines work

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Vaccines work by imitating an infection or disease and stimulating the immune system to develop antibodies.

Antibodies are the body's way of protecting us against disease or infections.

The antibodies produced by vaccines fight disease without actually infecting us with the disease.

If a vaccinated person comes into contact with the disease, their immune system will recognise it and immediately produce the antibodies they need to fight it.

Newborn babies are protected against several diseases, such as measles, mumps and rubella, because antibodies have passed to them from their mothers.

This is called passive immunity. Passive immunity usually only lasts for a few weeks or months.

In the case of measles, mumps and rubella, it may last up to a year, which is why the MMR vaccine is given to children just after their first birthday.

How are vaccines made?

Vaccines are made using viruses or bacteria and weakening or inactivating (killing) them so they cannot replicate or trigger disease.

These are then combined with other vaccine ingredients, such as stabilisers and preservatives, to produce a vaccine.

Can you overload a child's immune system?

As soon as a baby is born, they come into contact with large numbers of different bacteria and viruses every day. Their immune system is designed to cope with this.

A child's immune system is not overloaded by the childhood vaccination programme.

Studies have shown there are no harmful effects from giving several injections of vaccines in one go.

The bacteria and viruses used in vaccines are weakened or killed, and there are far fewer of them than the bugs that babies and children come into contact with every day.

Vaccination helps to improve protection against life-threatening diseases at the right time.

How long does a vaccination last?

Some vaccines require a course to give best protection. For example, measles, mumps and rubella (MMR) requires 2 doses, whereas other vaccines can be given as a single dose.

How a vaccination programme works

When a vaccination programme is introduced, everyone of a certain age or in a certain risk group is offered a specific vaccine to try to reduce the number of cases of the disease.

Vaccination programmes aim to protect people for life. They often concentrate on young children as they're at risk of many potentially dangerous infections.

Some vaccination programmes are for older people, such as the shingles vaccine.

Other programmes are for certain risk groups, such as healthcare workers and the hepatitis B vaccine

When a vaccination programme against a disease begins, the number of people catching the disease goes down.

But it's important to keep vaccinating, otherwise the disease can spread again.

If enough people in a community are vaccinated, it's harder for a disease to pass between people who have not been vaccinated. This is called "herd" or population immunity.

Herd immunity is particularly important for protecting people who cannot get vaccinated because they're too ill or because they're having treatment that damages their immune system.

Public Health England (PHE) records the vaccinations that adults and children receive. PHE also records the number of cases of each disease each year.

This way, PHE can work out the effect each vaccination has on a particular disease.

This helps the Joint Committee on Vaccination and Immunisation (JCVI) decide whether the routine vaccination programme needs to change.

Getting rid of disease

As more people are vaccinated, the disease can sometimes disappear completely and the vaccination programme can be stopped. This has happened with smallpox.

If a disease is highly infectious, more people will have to be vaccinated against it to keep the disease under control.

Measles, for instance, is highly infectious. If the number of people who have MMR goes down, measles will quickly spread again.

We know at least 90% of children have to be immune to stop a disease spreading. If 95% of children are protected by MMR, it's possible to get rid of measles.

Page last reviewed: 26/03/2019
Next review due: 26/03/2022