I remember reading a book about two years ago, but I can't remember the name. It's a young adult book, and I know there are at least two books in the series.
One of the main characters is a boy whose name I don't know; he might be telling the story, I'm not sure. I think he has an older brother. There are monsters that are like zombies; they might be all the adults over 18.
The main setting is a school with other children and they have to block the doors and windows. He also sees his teachers who have become monsters. I don't really remember anything else, so if you have heard of this, can you please tell me?