What I'm puzzled about is how these children got into school? I know mine had to be immunized before they got in. Although one of mine didn't get the last booster shot(for reasons I can't remember), she did get all of those until then. And we did catch them up when she went into High School! They insisted on it! Though I can't understand why they didn't say anything about the last booster before she got in.
You can easily get a waiver these days for religious or medical reasons.