How Vaccines Work

What is Immunity?

When disease germs enter your body, they start to reproduce. Your immune system recognizes these germs as foreign invaders and responds by making proteins called antibodies. These antibodies’ first job is to help destroy the germs that are making you sick. They can’t act fast enough to prevent you from becoming sick, but by eliminating the attacking germs, antibodies help you to get well.

The antibodies’ second job is to protect you from future infections. They remain in your bloodstream, and if the same germs ever try to infect you again — even after many years — they will come to your defense. Only now that they are experienced at fighting these particular germs, they can destroy them before they have a chance to make you sick. This is immunity. It is why most people get diseases like measles or chickenpox only once, even though they might be exposed many times during their lifetime.

Vaccines to the Rescue

Vaccines offer a solution to this problem. They help you develop immunity without getting sick first.

Vaccines are made from the same germs (or parts of them) that cause disease; for example, polio vaccine is made from polio virus. But the germs in vaccines are either killed or weakened so they won’t make you sick.

Vaccines containing these weakened or killed germs are introduced into your body, usually by injection. Your immune system reacts to the vaccine in a similar way that it would if it were being invaded by the disease — by making antibodies. The antibodies destroy the vaccine germs just as they would the disease germs — like a training exercise. Then they stay in your body, giving you immunity. If you are ever exposed to the real disease, the antibodies are there to protect you. 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