, confirming the severity of the reaction and the associated high mortality rate.
The new series comes from an international registry of consecutive patients who experienced CVST within 28 days of COVID-19 vaccination between March 29 and June 18, 2021, from 81 hospitals in 19 countries.
The cases are described in an article published online on Sept. 28. in JAMA Neurology.
“This is a reliable description on the clinical condition of these patients with CVST associated with COVID-19 vaccination. It is striking that this a much worse condition than CVST not associated with COVID-19 vaccination, with a much higher rate of intracerebral hemorrhage and coma and a much higher mortality rate,” senior author Jonathan M. Coutinho, MD, Amsterdam University Medical Centers, told this news organization.
These data confirm the observations from an earlier U.K. cohort in which cases of cerebral venous thrombosis linked to COVID-19 vaccination occurred.
“This is the biggest series, and as an international series, it gives a broader perspective from a larger range of countries,” Dr. Coutinho said. “All the data together show that, although this side effect is rare, the consequences are very severe,” he added.
In the current study, the researchers regarded CVST as being linked to the vaccine if it was accompanied by thrombosis with thrombocytopenia syndrome (TTS), as evidenced by thrombosis and new-onset thrombocytopenia.
In the cohort of 116 patients with CVST after COVID-19 vaccination, 78 (67.2%) had thrombosis with TTS and were thus classified as having had a vaccine-related adverse event. These patients were frequently comatose at presentation (24%) and often had intracerebral hemorrhage (68%) and concomitant thromboembolism (36%); 47% died during hospitalization.
These patients were compared with the 38 patients in the same cohort who had CVST but in whom there was no indication of concomitant thrombosis and thrombocytopenia. The case patients were also compared with a control group of 207 patients with CVST who were included in a separate international registry before the COVID-19 pandemic.
Mortality rates were much higher among the patients deemed to have had a vaccine-related CVST. The in-hospital mortality rate was 47%, compared with 5% among the patients in the same cohort who did not have TTS and 3.9% among the prepandemic control group.
The mortality rate was even higher (61%) among patients in the TTS group for whom the diagnosis was made before the condition garnered attention in the scientific community. The mortality rate was 42% among patients diagnosed later.
Of the 78 patients in whom CVST and TTS occurred after COVID-19 vaccination in this cohort, 76 had received the AstraZeneca vaccine (in 75 patients, CVST and TTS occurred after the first vaccination; in one patient, they occurred after the second vaccination). One patient had received the Johnson & Johnson vaccine, and one had received the Pfizer vaccine.
“After more analysis, the case after the Pfizer vaccination is not believed to be caused by the vaccine,” Dr. Coutinho said. “In that case, the patient had a platelet count just below the lower limit and was taking an immunomodulator drug that is known to be associated with thrombocytopenia.”
For two patients who received the AstraZeneca vaccine, there was also an alternative explanation for the thrombocytopenia.
Dr. Coutinho also pointed out that the Johnson & Johnson vaccine has been used mainly in the United States, and these data were largely from other countries.
The median time from vaccination to CVST symptom onset was 9 days in the TTS group. The median platelet count at hospital admission among patients with postvaccination CVST-TTS was 45. Three patients presented with a normal platelet count and developed thrombocytopenia during admission; two patients presented with mild thrombocytopenia, 30 presented with moderate thrombocytopenia, and 43 presented with severe thrombocytopenia.
Antibodies against platelet factor 4 (PF4) were measured in 69 patients with TTS, of whom 63 (91%) tested positive (the one patient in whom TTS occurred after the patient received the Pfizer vaccine did not test positive). However, the researchers note that sensitivity varies among different PF4 ELISA tests. Findings of platelet activation assays were positive in all 36 tested patients.
In the TTS group, 52 patients (67%) received immunomodulation therapy, most often intravenous immunoglobulins (IVIG). Among patients treated with IVIG, the mortality rate was lower (28%).