You might not know if they did. A lot of health problems that our friends experienced after the shots can be hidden. Messed up periods, getting COVID repeatedly (like 3x a year), difficulty doing exercise and so on. If someone trusts you, they might talk to you about them. If you've been praising the wonderful science then they aren't gonna open up because why would they? They already know you'll tell them it's all just a coincidence and won't be sympathetic anyway.