An adverse reaction is any reaction to a medication other than it's intended effect. That reaction can be hemorrhaging from the eyeballs and bleeding out, or it can be nothing at all, if it was anything other than the intended effect, it counts as an adverse reaction, and anyone who works for a pharma company has to report it. So if I'm talking with some guy at a picnic and I find out he's taking a blood pressure medication made by my company, I have to ask him how it's working for him. If he tells me it's doing anything besides lowering his blood pressure, I have to report it. If it's doing literally nothing to him, I have to report it. This is SOP across the entire pharmaceutical company that wants the FDA to even look at them.
I apologize for keeping it brief, but it leads me to this point: pharmacovigilance is something everyone takes deadly serious, to the point a company wants everyone working for it to let them know if one of their drugs so much as gives someone the runs. Yet here we have media and big tech companies censoring any and all adverse reactions to the covid vaccines that pop up. Twitter censoring video of that mother whose daughter was in a wheelchair on a breathing tube being just one of what I imagine are tens of thousands of examples of things that, with literally any other medication, pharma companies would be falling over themselves to find, track, and correct. That tells me all I need to know.