List of vaccine-associated signals (15 items)
Myocarditis (inflammation of heart muscle)
What: Chest pain, shortness of breath, palpitations.
Which vaccines: Mainly associated with mRNA vaccines (Pfizer-BioNTech, Moderna).
How common: Highest risk in young males after the 2nd dose — studies reported tens of cases per million doses in adolescent/young adult males (e.g., ~50–105 per million in some age-sex groups). In general adult populations estimates are lower (single-digit to low-double-digit cases per million). JAMA Network+1
Pericarditis (inflammation of the heart lining)
What: Chest pain relieved by sitting up, pericardial rub; often occurs with/after myocarditis.
Which vaccines: Also linked to mRNA vaccines.
How common: Similar order of magnitude to myocarditis but variable by age/sex; often mild and self-limited. PubMed+1
Guillain-Barré syndrome (GBS)
What: Progressive muscle weakness and numbness; can be severe.
Which vaccines: Signal stronger for adenoviral-vector vaccines (e.g., AstraZeneca / Vaxzevria, Johnson & Johnson) in several studies; less signal for mRNA vaccines.
How common: Rare — observed increases in some datasets within ~6 weeks after vaccination; absolute numbers are small but statistically detectable in large cohorts. PMC+1
Cerebral venous sinus thrombosis (CVT) / Thrombosis with thrombocytopenia (VITT/TTS)
What: Blood clots in brain veins sometimes accompanied by low platelet counts (can be life-threatening).
Which vaccines: Adenoviral-vector vaccines (AstraZeneca, Johnson & Johnson) were most commonly implicated in VITT/TTS reports.
How common: Very rare, but severe — prompted temporary pauses and age-specific recommendations in some countries when first identified. AHA Journals+1
Acute Disseminated Encephalomyelitis (ADEM) and other rare neuro-inflammatory events
What: Rare inflammation of brain and spinal cord; can cause neurologic deficits.
Which vaccines: Reported as a signal in some large-scale safety surveillance datasets (rare).
How common: Extremely rare — reported as safety signals requiring further study rather than confirmed causal relationships. PubMed
Immune thrombocytopenia (ITP) / Low platelets (non-VITT)
What: Low platelet counts leading to bleeding/bruising risk.
Which vaccines: Reports have appeared across vaccine types; some cases were transient.
How common: Rare; often manageable with standard therapies. ijmm.ir
Anaphylaxis / Severe allergic reaction
What: Rapid onset allergy (hives, breathing difficulties, hypotension).
Which vaccines: Reported with mRNA and other vaccines but overall extremely rare.
How common: Rare — vaccination sites monitor recipients for 15–30 minutes and are prepared to treat anaphylaxis immediately. PMC
