Patients will ask whether COVID-19 vaccines increase clot risk. This is due to reports of serious blood clots along with low platelets after the Johnson & Johnson/Janssen vaccine in the U.S and the AstraZeneca vaccine in other countries. Both are viral vector vaccines. Now the Janssen vaccine emergency use authorization (EUA) fact sheets will warn about this issue. Put the risk in perspective and continue to urge patients to get immunized with ANY COVID-19 vaccine.
Emphasize that these clots are RARE with just a handful of cases to date in about 8 million doses of the Janssen vaccine given in the U.S. Explain that the clot risk due to severe COVID-19 is MUCH higher. Reinforce that there are NO reports of this issue with the Pfizer-BioNTech or Moderna mRNA vaccines after over 200 million doses.
Be aware, most clots with the Janssen or AstraZeneca vaccines are unusual, cerebral venous sinus thrombosis in the brain or splanchnic vein thrombosis in the abdomen, along with thrombocytopenia. The theory is that an immune response to the vaccine may promote this “thrombosis with thrombocytopenia syndrome (TTS)” similar to autoimmune heparin-induced thrombocytopenia (HIT). Most reports with the Janssen vaccine are in females under age 50, about 1 to 2 weeks after vaccination. Reassure that there’s little concern about clotting if the vaccine was given over 3 weeks ago.
Don’t use aspirin or another antithrombotic for prophylaxis. There’s no evidence this helps, and it may increase bleeding risk. But tell patients to seek prompt medical care if they have symptoms such as severe headache or abdominal pain, blurred vision or petechiae, especially within 3 weeks of the Janssen vaccine. If these patients have a clot and thrombocytopenia, work with hematology. Don’t start heparin or low-molecular-weight heparin. Treat similar to HIT and add intravenous immune globulin (IVIG). Continue to report serious adverse events and administration errors to the Vaccine Adverse Event Reporting System (VAERS). Point out that safety systems are working as they should to catch potential issues.
REFERENCES
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MacNeil, J.R. (2021). Updated Recommendations from the Advisory
Committee on Immunization Practices for Use of the Janssen (Johnson
& Johnson) COVID-19 Vaccine After Reports of Thrombosis with
Thrombocytopenia Syndrome Among Vaccine Recipients — United States,
April 2021. MMWR. Morbidity and Mortality Weekly Report, [online] 70. Available at: https://www.cdc.gov/mmwr/volumes/70/wr/mm7017e4.htm?s_cid=mm7017e4_w
CDC. HAN Archive - 00442 | Health Alert Network (HAN). [online] Available at: https://emergency.cdc.gov/han/2021/han00442.asp.
Greinacher A, Thiele T, Warkentin TE, Weisser K, Kyrle PA, Eichinger S. Thrombotic Thrombocytopenia after ChAdOx1 nCov-19 Vaccination. N Engl J Med. 2021 Apr 9:NEJMoa2104840. Available at: https://www.nejm.org/doi/full/10.1056/NEJMoa2104840Schultz NH, Sørvoll IH, Michelsen AE, Munthe LA, Lund-Johansen F, Ahlen MT, Wiedmann M, Aamodt AH, Skattør TH, Tjønnfjord GE, Holme PA. Thrombosis and Thrombocytopenia after ChAdOx1 nCoV-19 Vaccination. N Engl J Med. 2021 Apr 9. Available at: https://www.nejm.org/doi/full/10.1056/NEJMoa2104882
Scully, M., Singh, D., Lown, R., Poles, A., Solomon, T., Levi, M., Goldblatt, D., Kotoucek, P., Thomas, W. and Lester, W. (2021). Pathologic Antibodies to Platelet Factor 4 after ChAdOx1 nCoV-19 Vaccination. New England Journal of Medicine. Available at: https://www.nejm.org/doi/full/10.1056/NEJMoa2105385