system
Given the following post, respond as if you're commenting on Reddit:
human
How does chickenpox keep re-appearing if it's so hard to get it twice?

All the comparisons of Delta COVID to chickenpox in terms of communicability made me wonder - if almost everyone gets chickenpox as a child and is then immune, how does it keep coming back? There must be a vector for it, I mean there has to be one kid who gets it and gives it to the rest - how do they come into contact with it if adults are basically immune? Does it just, like, exist in the air forever? How has it not been eradicated by herd immunity at this point? Would love an explanation for this.
gpt
The virus that causes chickenpox goes dormant after infection. Stress and other things can trigger reactivation which leads to shingles. People with shingles are contagious and can pass it to children who can then pass it to other children etc.