The Centers for Disease Control and Prevention said Wednesday it had identified a total of 28 cases of serious, potentially life-threatening blood clots among the more than 8.7 million people who had received the Johnson & Johnson Covid-19 vaccination.
This latest case count is as of May 7. Previously, as of April 25, the CDC had reported 17 cases of the clots out of nearly 8 million people given the shots.
The CDC and the Food and Drug Administration paused use of the Johnson & Johnson vaccine April 13 after reports of the very rare but dangerous blood clots. The pause was lifted April 23.
In all 28 cases, the patients received the shots before the April 13 pause, Dr. Tom Shimabukuro, who leads the CDC’s Covid-19 vaccine safety monitoring work, said. He provided an update on the cases Wednesday at a meeting of the CDC's Advisory Committee on Immunization Practices, a group of independent advisers.
Current evidence "suggests a plausible causal association" with the Johnson & Johnson vaccine and the cases of thrombosis with thrombocytopenia syndrome, or TTS, Shimabukuro said. The condition involves blood clots accompanied by a low level of platelets — the components in the blood that help it to clot.
The events appear similar to what is being observed following administration of the AstraZeneca Covid-19 shots in Europe, he added.
Most of the Johnson & Johnson cases in the United States were among women ages 18 to 49, the CDC said. Just six cases were in men. Rates among women ages 30 to 39 and 40 to 49 were particularly high, according to the presentation, at 12.4 cases per million and 9.4 cases per million, respectively.
Onset of TTS occurred three to 15 days after vaccination, with a median onset of nine days. “Most of the cases have a symptom onset after vaccination around one to two weeks,” Shimabukuro said.
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Nineteen of the patients developed a type of brain blood clot called a cerebral venous sinus thrombosis, or CVST. Four patients remain hospitalized, with one in intensive care. Two patients were sent to post-acute care facilities. Three patients died. Nineteen have been discharged home.
Shimabukuro noted that the use of heparin, a commonly used anticoagulant, to treat these patients dropped significantly after the CDC and the FDA paused the Johnson & Johnson vaccine. It is thought that treatment of TTS with heparin could make the condition worse, and at the onset of the pause, the CDC alerted health care providers to avoid use of heparin.
The syndrome does not appear to be associated with either of the Covid-19 vaccines produced by Pfizer-BioNTech or Moderna; Indeed, there were no confirmed reported cases of TTS after the 135 million Pfizer doses or the 110 million Moderna doses administered in the U.S.