On reading chapter books

So MM and I are reading More All-of-a-Kind-Family which is how I'm exposing him to Jewish Culture (hey, that's how I got it aside from the annual Passover Seder and Hannukah celebration). And we just hit the chapter where the Lower East Side is reeling from the Polio epidemic of 1916. And I realized that this may not be good bedtime fare for an imaginative 5-year-old. So I say to him,

"This chapter is about a sickness that was really, really bad.
BUT, you shouldn't think that this is an illness that YOU can
get because you can't. Do you know why?"

"Why?"

"Because the doctor gave you a vaccine that will protect
you from getting this sickness."

"What's a vaccine?"

"A vaccine is what you get when you get a shot at the doctor's office. You get the shot that teaches your body to fight the illness so you don't get sick. This is why Mommy and Daddy make sure that you get all the shots you need so that you won't get sick with Polio and Measles and other illnesses like that."

"Did you get those shots too?"

"Yes I did. But in 1916, when this story takes place, they didn't have the vaccine, so people got sick, and sometimes they died. OK?"

"Okay."

And then I read the chapter, and he was fine. But now the question is, Will Lena Marry Hyman? We'll find out tomorrow!