Perspective:

This paper provides mechanistic understanding to a rare but increasingly recognized complication of the AstraZeneca COVID-19 vaccine. Termed “vaccine-induced thrombotic thrombocytopenia” (VITT), this condition appears to occur within 1-3 weeks following vaccination and is associated with thrombotic events. These events are often in the cerebral venous sinus or splanchnic veins but can also be found in more traditional locations (e.g., lower extremity deep veins, pulmonary arteries) and in arterial beds (both peripheral and intracardiac). A key feature of this condition is the presence of thrombocytopenia and PF4-heparin autoantibodies that mimic heparin-induced thrombocytopenia (HIT). While the condition is quite rare, clinicians in countries where the AstraZeneca COVID-19 vaccine is being used must maintain a high degree of suspicion for patients who present with severe headache, nausea/vomiting, or other findings that could be linked to thrombotic events within 1-3 weeks after vaccination and are found to have thrombocytopenia. Use of nonheparin anticoagulants +/- intravenous immune globulin is critical and an ELISA test for PF4-heparin antibodies (such as is commonly used to diagnose HIT) should be performed. To date, this condition has not been recognized in association with the Pfizer or Moderna COVID-19 vaccines.

Update: On April 13, 2021, the Centers for Disease Control and Prevention (CDC) and Food and Drug Administration (FDA) announced a “pause” in the use of the Janssen/Johnson & Johnson COVID-19 vaccine related to six cases of cerebral sinus vein thrombosis and thrombocytopenia. These cases may be similar to the VITT condition being described in this N Engl J Med article. More information can be found at the CDC website: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/JJUpdate.html.