All the patients, as well as 17 others with clots after vaccination whose blood was tested, had antibodies known to activate platelets.
The antibodies led to a condition called thrombotic thrombocytopenia, which causes both clotting and abnormal bleeding. The researchers suggested naming the newly identified version in these patients “vaccine-induced immune thrombotic thrombocytopenia.”
The article described specialized blood tests that can be used to diagnose the disorder, and suggested treatment with a blood product called intravenous immune globulin, which is used to treat various immune disorders. Drugs called anti-coagulants, or blood thinners, can also be administered in some cases, but not a commonly used one, heparin — because the vaccine-related condition is very similar to one that occurs, rarely, in people given heparin.
The second report, from Norway, described five patients, one male and four female health care workers ages 32 to 54, who had clots and bleeding from seven to 10 days after receiving the AstraZeneca vaccine. Four had severe clots in the brain, and three died. Severe headaches were among their early symptoms. Like the German patients, all had high levels of antibodies that could activate platelets.
The team from Norway also recommended treatment with intravenous immune globulin. The researchers said the disorder was rare, but “a new phenomenon with devastating effects for otherwise healthy young adults,” and they suggested that it may be more common than previous studies of the AstraZeneca vaccine had indicated.
On Friday, European regulators also said they were reviewing reports of a few blood clot cases that occurred in people who had received the Johnson and Johnson vaccine. In the United States, federal agencies are investigating reports of a different type of unusual blood disorder involving a precipitous drop in platelets that emerged in a few people who had received either the Pfizer-BioNTech or Moderna vaccines.
Benjamin Mueller and Melissa Eddy contributed.