So how large do you think such a diagnosis effect may be? That other paper reported only 7% of clinical diagnoses were lab positive for measles in Singapore.

And yet another effect to deal with is that people used to spread measles on purpose:

“Before the introduction of measles vaccines, measles virus infected 95%–98% of children by age 18 years [1–4], and measles was considered an inevitable rite of passage. Exposure was often actively sought for children in early school years because of the greater severity of measles in adults.” http://jid.oxfordjournals.org/content/189/Supplement_1/S4.fu...

I think for these reasons it is clear the effectiveness of measles vaccines has been overstated, it is only a matter of how much.