Definition of categories of relation of adverse event to study vaccine administration
| Relation | Definition |
| Not related | The adverse event is obviously explained by another cause and/or the time of occurrence of the adverse event is not reasonably related to the vaccination |
| Remotely related | The adverse event is likely to be explainable by causes other than vaccination |
| Possibly related | Vaccine administration and the adverse event occurrence are reasonably related in time and the adverse event is explained equally well by causes other than vaccination |
| Probably related | Vaccine administration and the adverse event are temporally related and the event is more likely to be explained by the vaccine than by other mechanisms |
| Definitely related | Vaccine administration and the adverse event are temporally related and the adverse event is consistent with the pattern of other known vaccine related events |