You’re right. We have no data on how the first 5 billion doses have gone. We need to wait until we get to 10 billion doses to know for sure.
It's more about time than number of doses, was it safe, we should know in say 5 or 10 years time, remember your kids are about to be vaccinated. I don't expect there to be a problem we have created for ourselves, lets hope we are all right on that score. But to declare it's safe in just 6 months is a bit premature don't you think.
Science is wonderful, it's the dumb **** we do with that science.