The reason why one case of influenza does not confer lifelong immunity is that the virus tends to mutate overtime which makes it unrecognizable to the immune system.
Why is it difficult to get immunity to influenza?
Influenza is caused by a virus which tends to mutate overtime in order to stay ahead of medical technology.
As a result, this mutation makes the original virus unrecognizable to the immune system which would then be unable to fight it.
Find out more on natural immunity at https://brainly.com/question/21480961
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