There are numbers missing: the vast amount of people who don’t contract measles because they were vaccinated isn’t identified here – just those who contract it despite being vaccinated (which is a much smaller amount of the population). Of those, 1 in 5,000 will get Dawson disease.
This is why it jumps so much in unvaccinated populations.
The 1 in 5,000 number is of people who do contract measles even though they were vaccinated, which is very small compared to unvaccinated numbers.
There are 2 sets of numbers here, and it’s only talking about that subset. Does that make sense?