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28 cases of TTS confirmed after J&J vaccine

May 14, 2021

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Six males are among 28 patients who developed thrombosis with thrombocytopenia (TTS) after receiving Johnson & Johnson/Janssen COVID-19 vaccine, and three patients died, according to a federal vaccine safety expert.

“TTS is a rare, clinically serious and potentially life-threatening condition. Current evidence suggests a plausible causal association with the Janssen COVID-19 vaccine,” said Tom Shimabukuro, M.D., M.P.H., M.B.A., of the Centers for Disease Control and Prevention (CDC) COVID-19 Vaccine Task Force Vaccine Safety Team.

Dr. Shimabukuro reported the most recent data on the 28 confirmed cases at the May 12 meeting of the CDC’s Advisory Committee on Immunization Practices (ACIP). All of the cases occurred before the April 13 pause in administration of the vaccine, and most were among women ages 30-49, he said.

The pause was lifted on April 23, and the emergency use authorization for the vaccine now includes a warning of rare clotting events with low platelets, occurring primarily among women ages 18 to 49 years.

Over 8.7 million doses of J&J vaccine had been given as of May 7.

All three of the patients who died had signs of severe cerebral venous sinus thrombosis (CVST) on initial imaging, and all died within two days of presentation. None of the individuals had received heparin, which may be harmful for patients with TTS after COVID-19 vaccination. Nineteen of the 28 patients with TTS had CVST, Dr. Shimabukuro said.

Suspected cases of TTS following COVID-19 vaccination reported to the Vaccine Adverse Event Reporting System (VAERS) are investigated immediately and thoroughly, Dr. Shimabukuro said. FDA and CDC clinicians screen VAERS reports daily to identify potential TTS cases. Medical records are requested for all potential TTS case reports to confirm thrombosis with laboratory evidence of thrombocytopenia using a working case definition developed by the CDC. The definition includes two tiers:

  • Tier 1 TTS: Thrombosis is in an unusual location, including cerebral venous sinuses, portal vein, splenic vein and other rare venous and arterial thromboses. The patient also may have thrombosis in more common locations. The platelet count is less than 150,000 per microliter. A positive heparin platelet factor 4 (PF4) enzyme-linked immunosorbent assay (ELISA) heparin-induced thrombocytopenia (HIT) antibody test result is supportive but not required.
  • Tier 2 TTS: Thrombosis is in a common location only (e.g., venous thromboembolism, axillary vein thrombosis, deep vein thrombosis, pulmonary embolism, etc.); isolated acute myocardial infarction or ischemic stroke is excluded. The platelet count is less than 150,000 per microliter. A positive heparin PF4 ELISA HIT antibody result is required.

Of the 28 patients, 25 had symptoms that met the Tier 1 case definition, and three had symptoms that met the Tier 2 definition, Dr. Shimabukuro said.

“The clinical features of TTS following Janssen COVID-19 vaccination appear similar to what is being observed following AstraZeneca COVID-19 vaccination in Europe,” he said.

As of May 7, there were no confirmed cases of CVST with thrombocytopenia after receipt of either the Pfizer-BioNTech or Moderna COVID-19 vaccine. A total of 135.7 million doses of Pfizer vaccine and 110 million doses of Moderna had been given.

In addition to sharing information with patients before administering the Janssen vaccine, providers are reminded to note anxiety-related events after vaccination. According to a May 7 CDC MMWR report, five mass vaccination sites in different states reported clusters of anxiety-related events after receipt of the Janssen COVID-19 vaccine. Among the 64 anxiety-related events were 17 events of syncope after vaccination.

CDC authors noted that the single-dose Janssen COVID-19 vaccine may be a more attractive option to those with a needle aversion who may be predisposed to anxiety-related events after being vaccinated. Other possible anxiety-provoking stressors could include the ongoing pandemic and seeing other people being vaccinated at mass vaccination sites and on media reports.

Study authors wrote: “It is important that vaccination providers are aware that anxiety-related adverse events might be reported more frequently after receipt of the Janssen COVID-19 vaccine than after influenza vaccination and observe all COVID-19 vaccine recipients for any adverse reactions for at least 15 minutes after vaccine administration.”


Report cases of thrombosis with thrombocytopenia after COVID-19 vaccination to the Vaccine Adverse Event Reporting System at

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