"Can you still get measles after the MMR vaccination?
It’s extremely unlikely, but you need two doses of MMR to be fully protected. The first dose of the MMR jab protects 90% of those who receive it, and the second dose tops this up to 99% protection. Almost all of the children in the Welsh outbreak who caught measles were either completely unvaccinated or only partially vaccinated."
Assuming everyone was vaccinated then:
2000 people exposed, with 99% effectiveness of vaccine, yields about 20 people who will contract measles despite being vaccinated.
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From the National Health Service (UK):
http://www.nhs.uk/Conditions/vaccinations/Pages/measles-outb...
"Can you still get measles after the MMR vaccination?
It’s extremely unlikely, but you need two doses of MMR to be fully protected. The first dose of the MMR jab protects 90% of those who receive it, and the second dose tops this up to 99% protection. Almost all of the children in the Welsh outbreak who caught measles were either completely unvaccinated or only partially vaccinated."
Assuming everyone was vaccinated then:
2000 people exposed, with 99% effectiveness of vaccine, yields about 20 people who will contract measles despite being vaccinated.