Examples include the VAERS system (USA), EudraVigilance (EU) and the Yellow Card system (UK). As with severe disease and mortality associated with a recent positive SARS-COV-2 test, vaccine-associated events may result directly from the vaccine (the vaccine is causal) or reflect unrelated background disease that is not related to the vaccine. The voluntary or non-enforced nature of reporting also means that actual rates of reported events may represent only about 10% of the true rate.
These databases serve a vital function in identifying the occurrence of unusual events or higher than expected rates, spurring urgent investigation to ascertain the cause and, in some circumstances, a halting of or withdrawal of the vaccine. This is critical as mass vaccination moves beyond controlled trials into populations who differ from the clinical trial population, or where rare but critical events are likely to have been missed in the smaller trial group. The rise in reports of adverse events in these three databases since the introduction of COVID-19 vaccines, which were introduced after relatively short trial periods, is an example of these systems working, and is intended to trigger urgent action to review safety and potential causality.
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