Suggested criteria for labelling causality in neurological AEFI
| Causality label | Assessment criteria | Considerations for neurological AEFI |
| Probable | Typical time frame. AND No indication of an alternative aetiology. AND No risk factors. | For immune-associated AEFI, <6 weeks from vaccination. No risk factors or alternative aetiology identified by the means of clinical, laboratory, radiological and electrophysiological assessment, as indicated. |
| Possible | Plausible time frame, but outside of typical. AND/OR There may be an indication of an alternative aetiology and/or risk factors, but these are unlikely to explain the event. | For immune-associated AEFI, 6–12 weeks from vaccination. Presence of risk factors, such as a previous episode of Bell’s palsy in a patient with postvaccination Bell’s palsy. |
| Unlikely | Timeline not in keeping with prior established temporal associations AND/OR Alternative aetiology and/or risk factors fully explain the event. | For immune-associated AEFI, <24 hours or more >12 weeks from vaccination. Clear alternative aetiology, such as Campylobacter diarrhoea preceding GBS. |
AEFI, adverse events following immunisation.