Dear Simon le Fevre

You get immune to a virus like a cold virus by meeting it. And then your immune system gets to work.

Part of the immune system recognises that virus and learns what it's like and makes antibodies. (Hello. I've seen you before. I know how to fix you!) Antibodies are special proteins that are designed to catch onto exact viruses. Then other parts of your immune system collect up the antibodies with the virus attached to them and get rid of them.

There are other things whose job it is to collect up those complexes and deal with them.

The whole process is very complicated and we don't understand it fully yet. That's why we can't help people become immune to everything, like AIDS for instance.

But there are lots of diseases that people can be immunised against.

When the immune system doesn't work you get sick.

How sick you get depends on how quickly your immune system takes to get on to attacking the virus. On the whole, the longer it takes, the sicker you get in the meantime. If you've never met a bug like that before then it takes you a while, during which time the virus is causing all sorts of problems.

But once you get over the virus you'll have learnt to recognise that kind of virus. Then you'll never be really sick from a virus exactly like that again--unless something happens to interfere with your immune system like you get AIDS or you're on drugs that upset (depress) your immune system.

Yours sincerely 

Virginia R. Claire

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