Question

About a hundred years ago, when smallpox persisted, a group of people who had

this disease earlier and had survived it had no chance of suffering from it again. So

having the disease once was a means of preventing subsequent attacks of the same

disease.

i) Why does this happen? Explain.

ii) We can fool the immune system. Clarify

iii) Name this principle of prevention of disease.​

Answer 1

Explanation:

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