I saw some statistics on this yesterday -- if we vaccinate 1 million people, over the following month we can expect quite a few of them to have some sort of medical emergency, just because if you selection 1 million people at random, some will have medical emergencies. https://twitter.com/hilzoy/status/1339255347656224772

If your 1 million people are not entirely random, but are instead people who are over age 65 or who have a chronic condition that puts them at higher risk of COVID complications, the odds of medical emergencies goes up, obviously.

I saw a thread about this yesterday that gave very specific numbers and it was a pretty great thread that I did not RT because you had to actually read it to definitely grasp that it was NOT saying the vaccine would cause these adverse events.