Two patients without underlying risk factors developed deep vein thrombosis, 27 and 29 days, respectively, after receiving the AstraZeneca ChAdOx1 nCoV-19 vaccine. A clear association has now been established between the vaccine and what is referred to as vaccine-induced immune thrombotic thrombocytopenia (VITT), a condition with thrombosis in unusual sites, thrombocytopenia and bleeding (2–4). However, cases reported had occurred within 14 days of vaccination.
The clinical picture with VITT is unique and dramatic, and the two patients discussed here did not have the same clinical picture. The level of platelet antibodies was not elevated in the patient who was tested for this. Neither of the patients had headaches, one had petechiae in two fingers, bruising and three blue toenails, but otherwise no symptoms of coagulation disorders. Both had normal platelet counts. As the cause of VITT is unknown, other thromboembolic conditions or bleeding cannot be ruled out as being part of the overall clinical picture, although this may be less likely.
D-dimer is formed by the degradation of cross-linked fibrin. Elevated D-dimer levels are a non-specific finding that can be seen in conditions such as infection, trauma, pregnancy, cancer, disseminated intravascular coagulation and after surgery. D-dimer, on the other hand, has a high negative predictive value, i.e. normal concentrations rule out deep vein thrombosis with more than 90 % certainty in ambulant patients with clinical symptoms of thrombosis (5). In the cases in question, the D-dimer level was not elevated, and the diagnosis of deep vein thrombosis was made by ultrasound examination.
Both patients had low Wells scores, which means that, according to guidelines (6), they should not have been referred for an ultrasound examination. Most flow charts for patients with deep vein thrombosis would recommend discharge without treatment. The two patients would probably have gone undiagnosed had they not been doctors themselves and in a position to ask a colleague to perform an ultrasound examination. Very thought provoking.
COVID-19 infection is known to increase the risk of thrombosis (7). One study showed that Wells scores were unreliable for predicting pulmonary embolism in COVID-19 patients: 4 out of 12 patients with pulmonary embolism had a Wells score of 0 (8). Another study showed that high Wells scores were as common in COVID-19 patients without pulmonary embolism as in COVID-19 patients with pulmonary embolism (9). It is conceivable that the situation is also similar post-vaccination as for COVID-19 infection. Perhaps Wells scores do not have the same negative predictive value after vaccination? Symptoms of thrombosis after vaccination should probably be followed up somewhat more closely than indicated by the standard procedure.
In a scenario of extensive vaccination with new vaccines, it is vital that both patients and doctors are vigilant. Suspected new, unexpected or serious adverse effects must be reported.