Does “after vaccination” mean “caused by vaccination”?
No. Timing is relevant evidence, but sequence alone cannot establish causation.
Short answer
Why background rates matter
When many people are vaccinated, some illnesses will occur afterwards at the rate normally expected in the population. Investigators compare observed patterns with expected background rates and appropriate comparison groups.
What else is considered?
Assessment can include the timing and clinical pattern, alternative medical explanations, whether the event occurs more often than expected, whether findings are consistent across data sources, biological plausibility and whether risk changes with exposure.
Why suspected events should still be reported
Reporting systems are designed to collect suspicions even when causation is uncertain. That broad collection helps detect possible patterns. The investigation comes after the report.
Sources and further reading
WHO — causality assessment of adverse events following immunisation
Educational scope
This page cannot determine what caused an individual health event. Seek advice from a suitably qualified healthcare professional about personal symptoms or concerns.