Vaccine-induced immune thrombotic thrombocytopenia (VITT) has been reported in a patient after receiving two vaccines with a recombinant adenoviral vector encoding the spike glycoprotein of coronavirus disease (COVID-19) in Europe and the United States [1, 2]. Among approximately 12.7 million people who received ChAdOx1 nCov-19 (AstraZeneca) vaccines in Korea [3], we detected two cases of cerebral venous sinus thrombosis together with throm-bocytopenia and positive results for platelet factor 4 (PF4)–heparin antibody using enzyme-linked immunosorbent assay (ELISA). The fatality rate in our study was 50%. This study aimed to analyze a suitable prognostic factor through a central review of domestic cases and a literature review of overseas reports.

We reviewed two Korean patients and previously reported 42 patients [1, 4-6] with VITT onset after receiving AstraZeneca vaccines in this study. We excluded one reported case from England because PF4-heparin antibody was not detected using two ELISA methods [5]. In total, 44 patients were selected for inclusion in this analysis (Table 1), composed of 17 and 27 male and female patients, respectively, showing a female predominance, and with a median age of 36 years (range, 21–77 yr). Initial symptoms appeared at a median of 10 days after vaccination (range, 5–24 days). Symptoms were analyzed in only 10 patients; headache was the most common symptom related to cerebral venous thrombosis (CVT). CVT was detected in 29 patients, including the 2 Korean cases, which was the most frequent site in 66% of the total patients. Six patients showed combined cerebral hemorrhage among 29 CVT cases. Pulmonary embolism was diagnosed in 12 (27%) patients, and arterial and splanchnic vein thromboses were detected in 10 (23%) and 8 (18%) patients, respectively.

All cases showed decreased platelet counts and elevated D-dimer levels, both at initial presentation [5, 6] and during treatment [1, 4, 6]. The initial and nadir platelet counts were available for 26 and 21 cases, respectively. The median platelet counts (range) initially and at nadir were 35,000 (7,000–113,000) and 23,000 (8,000–107,000) (reference range, 150,000–440,000/mL). All except two cases had positive results for PF4–heparin antibody on ELISA, but the quantitative value did not correlate with the clinical outcome. Data on peak prothrombin

When comparing patients with favorable outcomes (recovery or full recovery) and those with unfavorable outcomes (fatal/died), the initial platelet counts between the groups were not significantly different in 26 patients, as determined using the nonparametric test (median, 35,500 and 23,000/mL). In contrast, the nadir platelet counts during the clinical course in 10 patients with favorable outcomes were significantly higher than those of 9 patients with unfavorable outcomes (median, 34,000 and 13,000/mL) (Fig. 1). The cutoff value for predicting fatality based on the nadir platelet count was 22,000/mL, as determined using a receiver operating characteristic curve, with an area under the curve of 0.928 (Fig. 2).

In Korea, adenovirus-based COVID-19 vaccines were banned for those in their 20s and permitted only for those ≥30-years-old since April 25, 2021, after performing the risk-benefit assessment when comparing severe hospitalization and mortality rates after COVID-19 with the predicted mortality of VITT [7]. Moreover, an active surveillance system involving a self-monitoring application that enabled early declaration and inspection was maintained for people receiving AstraZeneca and Janssen vaccines. Tests for the PF4-heparin antibody were performed in a central laboratory. Among the 35 suspected thrombocytopenia and/or thrombosis cases, two were confirmed as VITT [8]. The relatively low incidence of two VITT cases among 12.7 million individuals when compared with that in Western countries (348 cases among 14.3 million individuals receiving AstraZeneca vaccination in the UK, 32 cases among 10.2 million individuals receiving Janssen vaccination in the USA) [9, 10] should be considered when preparing the vaccination guidelines for each country.

Rapid deterioration and fatality due to VITT were the main problems during the early periods, until we elucidated the exact mechanism of the disease. The key patho-physiology causing both thrombosis and bleeding is based on an autoantibody-mediated immune response, similar to heparin-induced thrombocytopenia. Therefore, the induction of immune tolerance through the administration of immunoglobulin and steroids is recommended as an effective treatment. The administration of anticoagulants other than heparin and low-molecular-weight heparin should be considered to improve the clinical course of thrombosis [11]. However, this study revealed that patients with severe thrombocytopenia at presentation or patients who failed to recover their platelet counts during treatment with immunosuppressants and those who bypassed anticoagulants may have a poor prognosis. This is the first important and significant recommendation globally, although only a few VITT cases have been reported, and their numbers are smaller than those reported in each country’s media. Our study findings suggest the following recommendations: 1) Individuals who receive AstraZeneca and Janssen vaccines should be educated about visiting the hospital immediately if they experience symptoms possibly related to thrombosis and thrombocytopenia between 4 days and 4 weeks after vaccination (suspected cases). 2) Medical staff in hospitals, including primary clinics, should immediately request PF4/heparin antibody tests to the central laboratory if they screened cases of thrombocytopenia and thrombosis through blood and imaging tests (presumed cases). 3) Patients with thrombocytopenia and thrombosis with positive results for PF4/heparin antibody should be treated with immuno-globulins, steroids, and substitutive anticoagulants (confirmed cases). In conclusion, we cautiously suggest that early diagnosis of VITT after symptom development is the most important aspect in reducing VITT-related fatality. Furthermore, clinicians should consider more active measures, such as plasma exchange, early when they detect patients whose initial or subsequent platelet counts are less than 22,000/mL.