I saw that too. I didn't realize they could vaccinate that way..cross posted from incubators anon thread
in a video i saw on hatchery chicks they punch a whole in the eggs to incubate for mareks on day 18.
i have been thinking about the same thing ever since
I've read that you can make a small hole in the egg after they internally pip to help prevent suffocation and it does work, but there is also research that says that if you make a hole, the chick won't be motivated to externally pip. Because of this, I will only make a 'safety hole' if they have been internally pipped for too long.