system
Given the following post, respond as if you're commenting on Reddit:
human
How is it Chicken Pox can become lethal as you age but is almost harmless when your a child? 

I know Chicken Pox gets worse the later in life you get it but what kind of changes happen to cause this?
gpt
Herpes researcher here.  Unlike, your garden variety herpes simplex, varicella zoster (the virus that causes the disease) is not as well understood.  We know it goes latent in nerve cells, it's incredibly difficult to study in the lab because we don't have a good model organism or cell culture system.  

Here's what we do know: the first time you get infected, the disease is known as chicken pox.  The symptoms are fairly mild and spread throughout the body, but the important thing is that your immune system is usually able to control it.  To prevent itself from being eliminated, the virus travels up your nerves and shuts itself down to prevent being detected.

When you become older (the main group of people at risk is over 50), you're immune system isn't as effective as it once was.  Or your body is under a lot of stress, or you have HIV.  Regardless, that's what allows a small amount of virus to reactivate and make a lot of virus in a cluster of nerve cells.  That's why shingles is localized and the symptoms are more sever; it's all concentrated into one area.