1987? You posted a study from 1987?! Gracious. Are you on anti-vaxxer sites or something? Asking on account of how it's puzzling as heck as to why on earth anybody would just pull out a 1987 study like that. Now, did you read that whole study for yourself? I have to wonder if somebody else just told you what the study said. Asking on account of how I've seen that happen a bunch around here, where folks post a study all sure it holds up their argument, but then that study shoots down their claim. My guess is they don't read it themselves, they're trusting whatever anti-vaxxer site it was presented on, when it's been misrepresented. Not please note I'm not saying that you're lazy but there's definitely a lot of laziness like that with anti-vaxxers in their "research."
Your 1987 study says
It acknowledges that there were vaccine failures, meaning students who got the vaccines back in the 1960s / 1970s when they were babies but still contracted the measles in the 1980s during an outbreak.
The study talks about how the school having a nice high vaccination rate helped.
So the folks having been responsible back then in getting their kids vaccinated right helped to slow down the transmission.