Vaccines in the body

Selma has had the measles. It was tough, but now she's well again. And that's not all. She is now immune to measles. Because now, after the illness, there are memory cells in Selma's immune system.

They remember what the measles virus looks like, and if this kind of virus tries to enter Selma's body again, loads of antibodies will be produced in a flash. The virus will not have a chance. When Selma got ill, the immune system trained itself. It learned how to handle this kind of intruder. What if you could train the immune system, without having to feel that sick?

What if the immune system could be trained in a safe way, like when pilots practice in flight simulators? There is in fact such a way. This is Selma's cousin Nora. She is about to get an injection. In the syringe there are measles viruses that are weakened.

When the viruses are injected into Nora's body, they won't be able to cause her harm. They are too weak, but the immune system gets going anyway. It produces antibodies, and destroys the viruses. And it produces memory cells. The memory of the measles virus will always be there in Nora's body, even though she has never been ill.

This is a vaccine. A vaccine is like a medicine that you take before the illness for the disease never to break out. Sometimes you get a low fever or some nausea from the vaccine, as the immune system does its work. But this is a mild reaction, which is far more tolerable than the actual illness. And this illness - measles - Nora will be protected from.

She will be immune. But not all vaccines give immunity for life. Some, like the vaccine against tetanus, have to be renewed for the person to continue to be immune. There are vaccines against many illnesses - like rubella, mumps, or chickenpox - and each of these has its own particular vaccine. But we don't have vaccines for all diseases.

Malaria is an example of an illness that is common in some parts of the world, that still lacks a vaccine that works. And there are a small number of people who are not immune, even though they have had the vaccine. Children who are seriously ill, for instance with cancer, have immune systems that do not function properly. For these children, the measles virus is life threatening. But in the town where Nora lives, almost everybody is vaccinated against the measles.

And if they are vaccinated, they won't get ill, and then they won't spread the virus. So, the children with cancer will not have to encounter the virus. Although their immune systems are weakened, they are protected from the measles, because many people around them are vaccinated. This is called herd immunity. When Nora gets the vaccine, she does something good not only for herself, but for everybody else that she meets.

There you go. Now Nora is vaccinated. It hurt a little. But she will not have to go through the discomfort and danger that Selma had to endure when she got the measles. And she won't infect others.

All this thanks to an injection: a vaccination.