Comparison of vaccine-induced immune thrombocytopenia and thrombosis cases following two adenovirus-vectored COVID-19 vaccines.

Background: Vaccine-induced immune thrombocytopenia and thrombosis (VITT) was first described after administration of adenovirus-vectored COVID-19 vaccines including Ad26.COV2.S and ChAdOx1 nCoV-19. It is not known if the clinical characteristics and outcomes of VITT after Ad26.COV2.S and ChAdOx1 nCoV-19 vaccination are different. We assessed demographic and clinical characteristics, laboratory findings and outcomes in patients with VITT after each vaccine.

Methods: Spontaneous postmarketing reports of VITT after Ad26.COV2.S were identified from Janssen's Global Safety Database and classified using NICE criteria (n = 86). Cases after ChAdOx1 nCoV-19 were identified from a published case series (n = 220). The analysis is descriptive.

Results: The median age of patients with definite/probable VITT after Ad26.COV2.S or ChAdOx1 nCoV-19 vaccination is 43 and 48 years, respectively. Median time-to-onset is 11 days and 14 days post-vaccination, cerebral venous thrombosis (CVT) is present in 50.6% and 50%, and mortality is 30% and 22% of patients, respectively. Women make up 55.3% of cases after Ad26.COV2.S and 55% after ChAdOx1 nCoV-19, 74%/60% of CVT cases and 68%/62.5% of deaths. Patients present with severe thrombocytopenia, grossly elevated D-dimer, and most test positive for anti-platelet factor-4 antibodies. Patients with preexisting rare autoimmune diseases are observed despite the small sample sizes.

Conclusions: Within the limitations of the data, our study finds no strong evidence for a clinically relevant difference in VITT occurring after Ad26.COV2.S or ChAdOx1 nCoV-19. Observed differences in some parameters likely result from the demographic of the populations vaccinated, and the situational and reporting differences in how, when, and where patients were identified and treated.