Vaccine Questions
What do Yellow Card numbers mean?
They are counts of suspected adverse-reaction reports submitted to the MHRA—not counts of events proven to have been caused by a medicine or vaccine.
Short answer
A report count is not an incidence rate. It cannot show how common a confirmed side effect is without additional evidence and context.
What context is needed?
- How many people received the product?
- What period and population do the reports cover?
- What is the expected background rate of the event?
- Did publicity or policy changes affect reporting?
- Has the MHRA or another regulator assessed causation?
- Do analytical studies support the suspected association?
Why the numbers are still useful
Spontaneous reports can reveal unusual patterns, rare events or changes in reporting that deserve investigation. Their strength is signal detection. They should neither be dismissed nor treated as confirmed causal cases.
Sources and further reading
Educational scope
This page explains report data generally. It does not determine whether a particular event was caused by a vaccine or medicine.