approx. 3.64 million U.S. children are vaccinated with a first dose of MMR every year which results in about 5,700 seizure, that's a rate of 0.0016 percent. OK, so lets say the following

5700/3640000=0.0016, percentage wise that is 100x0.0016=0.16 percent. That means that out of 10000 children 16 suffer seizures. That is not the whole story, as underreported and non reported cases are estimated at 10 to 1 and as much as 15 to 1.

0.6% of 3.64 million is 23k.