Why does one become immune and unable to pass on a certain disease after being infected by it?
In: Biology
[This graph](https://cnx.org/resources/567ad79b5a158e6b717fcccbc748466c/Figure_42_02_10.jpg) illustrates it nicely.
The first time you are exposed to something, your immune system is slow to respond and the response itself is small. The immune system has a memory, so the second time you are exposed to something the immune system will recognise it and the response is immediate and big. This can clear up the pathogen before you get sick so you may not even notice you were re-exposed. If it can’t take hold then you’re not carrying it around either.
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