How are severity, seriousness and expectedness different?

Why

A severe headache may require strong analgesia but not meet a serious-event criterion. A relatively mild symptom associated with a medically important intervention could nonetheless count as serious. Seriousness typically considers death, life threat, hospitalisation or prolonged hospitalisation, disability, congenital anomaly and other important medical events under the applicable framework.

Severity describes the grade or intensity, often using a protocol-specific scale such as CTCAE where appropriate. Expectedness asks whether the nature or specificity of the suspected reaction is consistent with the controlling reference, which differs by setting and market. For example, an intense but already labelled nausea episode could be severe, non-serious and expected.

Another event could be serious despite moderate intensity. Evaluate and document each dimension independently before deciding reporting responsibilities and timelines. Do not equate a high severity grade with a legally defined serious adverse reaction.