How many IB students get a 45?

I'm curious, can you tell me how many International Baccalaureate (IB) students typically achieve a score of 45 out of the maximum 45 points? I understand that the IB program is rigorous and competitive, so it must be quite an accomplishment for students to attain such a high score. Is there a specific percentage of students who manage to do so, or does it vary greatly from school to school and year to year?