J&J Vaccine: CVST, VITT, and What Physicians Should Do

Sandra Adamson Fryhofer, MD


April 20, 2021

This transcript has been edited for clarity.

This edition of Medicine Matters addresses new safety concerns for Janssen's viral vector vaccine: what to look for, what to do, what not to do, and what to tell your patients.

Here's the timeline:

On February 27, 2021, the FDA authorized the emergency use of Janssen viral vector COVID-19 vaccine for those 18 and older. (Janssen is the pharmaceutical arm of Johnson & Johnson.)

As of April 12, 2021, more than 6.8 million doses of the Janssen vaccine have been administered in the United States.

On April 13, 2021, the FDA and CDC issued a joint statement calling for a pause in Janssen vaccine administration when a safety signal from CDC's Vaccine Adverse Event Reporting System revealed a curious and concerning combination: six patients with cerebral venous sinus thrombosis (CVST) in combination with thrombocytopenia.

All six patients were women, age 18-48. One of them has died. All six patients had received Janssen's single-dose viral vector COVID vaccine within the previous 2 weeks. These findings were foreshadowed by recent European reports of unexpected blood clots in patients within weeks of receiving another viral vector vaccine, by AstraZeneca. AstraZeneca's vaccine has not yet been authorized in the United States.

What does the 'pause' mean?

This pause is a recommendation, not a mandate. It's being made out of an abundance of caution. It demonstrates honesty and transparency, and should inspire confidence in the process. A safety signal was identified. CDC and FDA acted quickly and issued a joint statement. CDC also issued a health alert through its Health Alert Network (HAN).

The Advisory Committee on Immunization Practices (ACIP) convened an emergency meeting on April 14, 2021 , to review these safety concerns. No action was taken; more data were needed. So, the pause continues for now, but not indefinitely. The plan is for ACIP to reconvene in 7-10 days. This will give CDC more time to identify specific risk factors (age, gender, and other factors, such as the use of estrogen-containing products like birth control pills or hormone replacement therapy).

This allows time to fully assess those already vaccinated and to see whether increased awareness triggers the reporting of more cases, which could be identified in the coming days and weeks.


CVST is very rare. The background rate of CVST is somewhere between 2 and 15 cases per million people, but that includes patients with a normal platelet count. The combination of the conditions (blood clots and low platelets) is the red flag and looks very similar to what has been recently reported in Europe with the AstraZeneca vaccine. The proposed syndrome linked to the AstraZeneca vaccine has been given the acronym VITT (vaccine-induced thrombotic thrombocytopenia). Recent reports in The New England Journal of Medicine suggest that this syndrome is similar to autoimmune heparin-induced thrombocytopenia (HIT).

What should we tell our patients and who should be concerned?

Those who received the Janssen vaccine in the past few weeks are still in the window of risk. Patients who received the Janssen vaccine within the past 3 weeks should seek medical care if they experience any of the following symptoms: severe headache, abdominal pain, leg pain, leg swelling, or shortness of breath. Patients should also look for petechiae or unexplained bruising.

Remind patients who have received any COVID vaccination that they can expect symptoms including mild to moderate headache, fatigue, fever, and muscle aches. These symptoms usually resolve within a few days.

Thrombosis? Low platelets? Ask about recent COVID-19 vaccination.

If you have a patient with blood clots, do appropriate imaging. Usually when we detect blood clots, we turn to blood thinners like heparin. Not here. For the type of blood clots associated with the viral vector vaccines, standard treatments like heparin could cause tremendous harm.

Check a CBC with platelet count. If the platelet count is low, get a platelet factor 4 (PL4) antibody test to look for platelet-activating antibodies. (CDC says the ELISA test version is best.)

CDC made clear recommendations in a recent HAN alert:

  • Do not treat patients with thrombotic events and thrombocytopenia following receipt of Janssen COVID vaccine with heparin unless HIT testing is negative.

  • If HIT testing is positive or if you can't run this test, non-heparin anticoagulants and high-dose intravenous immune globulin should be considered.

CDC recommends consulting a hematologist immediately.

Is this new signal a needle in a haystack or the tip of the iceberg?

Some might say that this pause is an overreaction. It has affected only one in a million vaccine recipients so far. Others point out that this is a rare but serious disorder. Vaccine safety is a primary concern. Janssen's vaccine can be stored at regular refrigerator temperatures for up to 3 months, which allows time to pause for further investigation before vaccine doses expire.

Unlike some other countries, the United States has authorized two other highly effective COVID vaccines which use a completely different platform. Current projections predict that supplies of both mRNA vaccines are fairly stable for the near future. As of April 14, 2021, CDC says there have been no reports of CVST combined with thrombocytopenia in patients who have received mRNA vaccines by Pfizer or Moderna.

For Medicine Matters, I'm Dr Sandra Fryhofer.

Follow Medscape on Facebook, Twitter, Instagram, and YouTube


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.