In my own experience, I have not actually seen this happening. Usually it is done in the form of a group, so if a nurse or doctor noticed an adverse effect, they would discuss it with each other. After that, it would be reported.
If you were taking a scenario in which one person had not reported, I've seen that the other person would report. For example, if a doctor missed an adverse effect event, then the nurse would report it, or vice versa.