My niece got a full blown case of the measles form the vaccine. The doctor was a bit shocked. But law measle cases have to be reported to the CDC, which the doctor did. But CDC stats never recorded the case. Getting the measles from the vaccine doesn't count. See how that works?
Measles vaccines are attenuated -- which means it contains a live strain. If just a fraction of a fraction of this attenuated strain gets transmitted, some will ultimately mutate into alternate forms and reappear. Giving such a large breeding ground to these viruses might eventually lead to a strain even worse than any known natural strain.
Things are rarely black-and-white, though most people seem to see it that way. It's dangerous when our leaders loose color vision, but it is easy to understand why. Just follow the green.