Address Concerns About Thrombosis With COVID-19 Vaccines

Patients will ask you whether COVID-19 vaccines increase clot risk.

This is due to reports of serious blood clots along with thrombocytopenia 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 ASAP 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 or splanchnic vein thrombosis, 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...and who are positive for heparin-platelet factor 4 (PF4) antibodies without heparin exposure.

Reassure that there's little concern about clotting if the vaccine was given over 3 weeks ago.

Look for patients presenting with symptoms such as severe headache or abdominal pain...blurred vision...or petechiae, especially within 3 weeks of the Janssen vaccine. Check for thrombocytopenia.

If patients have thrombocytopenia with thrombosis, order a heparin-PF4 enzyme-linked immunosorbent assay (ELISA) and involve hematology.

During the workup, use cautions similar to HIT. Don't start heparin or low-molecular-weight heparin...and stop warfarin.

Plan on using argatroban, bivalirudin, fondaparinux, or a DOAC. Also give high-dose intravenous immune globulin (IVIG)...such as 1 g/kg for 2 days...and avoid platelet transfusions unless there's bleeding.

Review our chart, Communicating About COVID-19 Vaccination, for more points to address vaccine hesitancy.

Key References

  • MMWR Morb Mortal Wkly Rep Published online Apr 27, 2021; doi:10.15585/mmwr.mm7017e4
  • https://emergency.cdc.gov/han/2021/han00442.asp (4-29-21)
  • www.hematology.org/covid-19/vaccine-induced-immune-thrombotic-thrombocytopenia (4-29-21)
  • N Engl J Med Published online Apr 9, 2021; doi:10.1056/NEJMoa2104882
  • N Engl J Med Published online Apr 9, 2021; doi:10.1056/NEJMoa2104840
  • N Engl J Med Published online Apr 16, 2021; doi:10.1056/NEJMoa2105385
Hospital Pharmacist's Letter. May 2021, No. 370501



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