#292 COVID-19 Vaccine Adverse Events
CLINICAL QUESTION
What does real world evidence tell us about adverse effects from available COVID-19 vaccines?
BOTTOM LINE
Best evidence finds systemic adverse events related to COVID-19 vaccines are mostly short-lived and differ by type of vaccine, dose given, age, and gender. Anaphylaxis to mRNA vaccines occurs in 2.5 to 5 per million doses. Vaccine-induced thrombotic thrombocytopenia (VITT) is associated with viral vector vaccines (AstraZeneca or Johnson and Johnson). Best estimates of incidence: ~0.5 to 2 per 100,000 and more commonly in women.
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EVIDENCE
- From published prospective or retrospective cohort/case control studies.
- General systemic adverse events:
- Best evidence from solicited adverse events up to 8 days post-dose in 655,590 patients with Pfizer (2 doses) or AstraZeneca (1 dose) adults:1
- Most commonly short lived and last 1-2 days:
- Fatigue, headache: Each 13-23%.
- Adverse events more common among:
- Recipients of AstraZeneca (versus Pfizer), Pfizer second dose versus first.
- Individuals 55 or younger.
- Women.
- Similar findings in clinical trials.2
- Anaphylaxis risk: Based on ~10 million Pfizer doses, ~8 million Moderna.3
- Incidence (per million doses): 5 (Pfizer), 2.5 (Moderna).
- 1/3 reported previous anaphylaxis episodes, ~80% with known allergies.
- No deaths reported.
- Incidence (per million doses): 5 (Pfizer), 2.5 (Moderna).
- Most commonly short lived and last 1-2 days:
- Best evidence from solicited adverse events up to 8 days post-dose in 655,590 patients with Pfizer (2 doses) or AstraZeneca (1 dose) adults:1
- VITT:
- VITT leading to rare thromboses, particularly cerebral venous sinus thrombosis (CVST), 4-28 days post AstraZeneca vaccine.
- Risk varies4,5 from 0.4 per 100,000 in 80+ years to ~2 per 100,000 in 20-49.
- Majority in women under 60 within 14 days of vaccination.5
- Cohort of 281,264 AstraZeneca recipients in Denmark/Norway6 calculated thrombosis events in excess of natural background risk:
- Additional venous thromboembolisms (includes deep venous thrombosis, pulmonary embolism and CVST) possibly attributed to vaccine: 11 per 100,000 doses and mostly in women.
- VITT leading to rare thromboses, particularly cerebral venous sinus thrombosis (CVST), 4-28 days post AstraZeneca vaccine.
- Suspect VITT if AstraZeneca or Johnson & Johnson vaccine 4-28 days prior, signs/symptoms or positive imaging of serious thrombosis with thrombocytopenia.7
- Diagnosis confirmed with positive heparin-induced thrombocytopenia assay.4,7
- Clinical pathways available to guide approach to suspected VITT8: https://is.gd/71P7I2
- Patient decision tool for AstraZeneca vaccine available:9 https://is.gd/Bn4EPJ
- To report possible vaccine related adverse events in Canada:10 https://is.gd/LwKQNDl
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