99.9% is so amazing! Only 1 person in 1000 isn't perfectly immune. And some reports and studies even say 100%. It all depends how you calculate the numbers. Some people say it's closer to 10%, using the same data but calculated another way. So the method or arriving at that number is really important. The drug companies seem to be coming to higher numbers than independent calculations.
If we see outbreaks of 22 people where almost all of them are vaccinated, that shows it's nowhere near 99.9% in real life.
What brand were the 22 given? Mostly Pfizer and Moderna, with a few AZ.