Vaccine safety: distinguishing seriousness from intensity

In a pharmacovigilance report, ‘serious’ has a regulatory definition. It does not simply mean ‘felt very strongly’. ANSM’s good practice guidance distinguishes seriousness from severity, meaning clinical intensity and its effect on the person.

The definition of a serious adverse reaction includes death, a life-threatening effect, significant or lasting disability, an effect causing or prolonging hospitalisation and a congenital abnormality. A healthcare professional can also judge an effect serious. Classification therefore requires information about its consequences.

Intensity describes a different dimension: how clinically marked a reaction is and how it affects the person. Describing an effect as mild, moderate or intense is not, on its own, enough to decide whether it meets regulatory seriousness criteria.

The cited flu vaccine product information and leaflet use ‘mild to moderate’ to describe the intensity of most effects observed in their data. This illustrates the vocabulary; it does not predict an individual reaction or replace medical assessment of symptoms.

If a report mentions ‘serious’ or an intensity grade, ask the professional which criteria or consequences led to that classification. To describe your situation, report the symptoms and their actual impact rather than assigning yourself a regulatory category.

Never delay care while choosing the correct word. The leaflet calls for immediate medical attention for an allergic reaction, including difficulty breathing or swelling of the throat or tongue. Checking seriousness or intensity comes after responding to an urgent medical need.