Known Adverse Events
Officially recognised vaccine adverse events — what the evidence shows and how causation is established
Not all adverse events reported after vaccination are caused by vaccines. Establishing causation requires rigorous scientific review. This page documents adverse events for which strong causal evidence exists — recognised by the CDC, FDA, WHO, and the Brighton Collaboration.
Transparent acknowledgment of documented risks is essential to this site's credibility. Vaccines carry real, documented risks. They also carry real, documented benefits. Both are presented here.
How Adverse Events Get Officially Recognised
Signal Detection
Passive surveillance systems like VAERS identify unusual patterns. Active systems like VSD and BEST confirm whether event rates exceed background expectations. A confirmed signal triggers formal investigation.
Causality Assessment
The Brighton Collaboration provides standardised case definitions. WHO's causality assessment framework classifies events as consistent causal, inconsistent causal, indeterminate, or unclassifiable.
ACIP & Regulatory Review
The CDC's Advisory Committee on Immunization Practices reviews evidence and updates recommendations. The FDA updates vaccine labelling to reflect confirmed adverse events.
VICP Recognition
The Vaccine Injury Compensation Program (VICP) Vaccine Injury Table lists conditions presumed to be caused by specific vaccines for compensation purposes. Inclusion reflects legal presumption, not always full scientific consensus.
Established Causal Associations
Documented Vaccine Adverse Events
| Adverse Event | Associated Vaccine(s) | Estimated Rate | Status |
|---|---|---|---|
| Anaphylaxis | Multiple vaccines | 1–2 per million doses | ✅ Established |
| SIRVA (Shoulder Injury) | Any injected vaccine | Rare — technique error | ✅ Established |
| Febrile seizures | MMR, MMRV | 1 per 3,000 (MMRV dose 1) | ✅ Established |
| Intussusception | RotaShield (withdrawn 1999) | ~1 per 10,000 | ✅ Established — led to withdrawal |
| Myocarditis/Pericarditis | mRNA COVID-19 vaccines | 1–105 per million doses | ✅ Established |
| Thrombosis with Thrombocytopenia (TTS) | AstraZeneca, J&J COVID-19 | 1–48 per million doses | ✅ Established — led to restrictions |
| Guillain-Barré Syndrome (GBS) | 1976 swine flu vaccine; J&J COVID-19 | ~1–2 per million doses | ✅ Established for specific vaccines |
| Immune Thrombocytopenic Purpura (ITP) | MMR | ~1 per 25,000 doses | ✅ Established |
Table note: Rates are estimates from post-licensure surveillance. For myocarditis detail see: Myocarditis & mRNA.
Important Context
- All rates listed are rare to very rare — most are measured in events per million doses
- For most listed adverse events, the risk from the vaccine-preventable disease exceeds the risk from vaccination
- Regulatory action (label updates, restrictions, withdrawals) demonstrates that safety monitoring systems work as intended
- The RotaShield withdrawal (1999) and AstraZeneca/J&J restrictions are examples of the system detecting and acting on real signals
- This table reflects currently recognised associations — ongoing research may update entries as evidence develops
How to Report a Suspected Adverse Event
- United States: Report to VAERS at vaers.hhs.gov or call 1-800-822-7967
- United Kingdom: Yellow Card scheme at yellowcard.mhra.gov.uk
- European Union: Contact your national competent authority or via EudraVigilance
- Healthcare providers: Mandatory reporting requirements apply — consult the VAERS Reportable Events Table for timeframes
Sources & Citations
CDC. "VAERS Table of Reportable Events Following Vaccination."
https://vaers.hhs.gov/docs/VAERS_Table_of_Reportable_Events_Following_Vaccination.pdfCDC. "Myocarditis and Pericarditis After COVID-19 Vaccination."
https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/myocarditis.htmlBrighton Collaboration. "Standardised case definitions for adverse events following immunization."
https://brightoncollaboration.us/brighton-collaboration-case-definitions/EMA. "COVID-19 Vaccine AstraZeneca: PRAC recommendations on signal." 2021.
https://www.ema.europa.eu/en/news/astrazeneca-covid-19-vaccine-prac-recommendations-signalHHS. "National Vaccine Injury Compensation Program Vaccine Injury Table."
https://www.hrsa.gov/vaccine-compensation/vaccine-injury-tableDeep Dives
Guillain-Barré Syndrome (GBS)
Evidence review of documented associations between specific vaccines and GBS, including the 1976 swine flu vaccine, 2009 H1N1, and the Janssen COVID-19 vaccine. Includes absolute risk context and regulatory assessments.
Anaphylaxis
Documented rates, risk factors, and standard observation protocols for anaphylactic reactions following vaccination. Includes comparison to anaphylaxis rates from other medical interventions.
Related Pages
Safety Overview
Overview of vaccine safety monitoring systems.
VAERS
US Vaccine Adverse Event Reporting System.
Myocarditis & mRNA
Evidence review of myocarditis and mRNA vaccines.
Global Reporting Systems
WHO AEFI and international pharmacovigilance.
VICP Program
National Vaccine Injury Compensation Program.
Vaccine Safety Timeline
A comprehensive chronological record of 60 documented vaccine safety events and regulatory responses, from 1798 to present. Every entry sourced from named primary documents.