Well yes, it is only a matter of time. After all the vax rate in Liverpool was 89% when they had that measles outbreak, ours is 90% and dropping.
If they made the shots single, wouldn't that just give the antivaxxers fodder so to speak? It would make them think, they were right, that something is awry with vaccines. When there just isn't the evidence to back them up.
It has been prove time and time again that there less adverse events with multi vaccines than with single vaccines. That is very telling to me.