Address Concerns About Clots 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 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 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 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.

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

Key References
  • MMWR Morb Mortal Wkly Rep Published online 2021 Apr 27; doi:10.15585/mmwr.mm7017e4
  • https://emergency.cdc.gov/han/2021/han00442.asp (4-27-21)
  • N Engl J Med Published online Apr 9, 2021; doi:10.1056/NEJMoa2104840
  • N Engl J Med Published online Apr 9, 2021; doi:10.1056/NEJMoa2104882
  • N Engl J Med Published online Apr 16, 2021; doi:10.1056/NEJMoa2105385
  • N Engl J Med Published online Apr 16, 2021; doi:10.1056/NEJMoa2106315
Prescriber's Letter. May 2021, No. 370501


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