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Important: VAERS reports alone cannot determine if a vaccine caused an adverse event. Reports may contain incomplete, inaccurate, or unverified information. Correlation does not equal causation.

Onset Calculator

Explore when vaccine adverse events typically occur. Select a vaccine to see the timing distribution of VAERS reports and understand onset patterns.

73%
of events within 3 days
Day 0
most common onset day
104
vaccines to explore
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Important Notes

  • • This tool shows when adverse events are reported, not when they necessarily begin
  • • Most vaccine side effects occur within the first few days after vaccination
  • • Timing patterns are similar across different vaccine types
  • • Not all VAERS reports include precise onset timing information