Difficult questions

Tuomas asked a difficult question yesterday:"Do angels get vaccinations?" followed by "do angels ever die?".

Risto is flying home tomorrow. He's feeling home sick every now and then, cried over the phone on Saturday. But my sister said that he's really enjoying his time there, so no worries. Yesterday he was worried that his plane would crash. I tried to convince him that it wouldn't happen.

Risto: "But planes do crash and people have died in plane crashes".
Me: "Yes, but it's highly unlikely". (Is there any point in explaining statistics to a six year old?)
Risto: "And what about the ship that sank, how many people died there?"
Me:"Which ship?"
Risto:"The one with four chimneys, that one!"
Me:"Titanic??!" (I don't remember telling him about the Titanic)
Risto:"Yeah, that one. How many people drowned?"
Me:"Oh, well, quite a few."
Risto:"How many people were saved?"
Me:"Very many people survived!!!! Oh, yes, many!" (This question was a relief!!!)

How do explain the death of hundreds of people? How do you explain the deaths caused by human cruelty, war? How do you explain the Holocaust? Would a vaccination help?