Cerebral venous sinus thrombosis may cause severe headache, stroke-like symptoms (weakness of a limb and/or facial muscles), seizures and coma. Splanchnic vein thrombosis may cause abdominal pain, accumulation of fluid in the abdominal cavity, and gastrointestinal bleeding.Other forms of thrombosis, such as the more common pulmonary embolism, may also occur. Arterial thrombosis has also been reported. The low platelet count may manifest as petechia (tiny blood spots under the skin) beyond the site of the injection.Disseminated intravascular coagulation (DIC), diffuse formation of blood clots throughout the blood vessels of the body, has been reported as part of the syndrome. DIC may cause a range of symptoms, including abnormal bleeding, breathlessness, chest pain, neurological symptoms, low blood pressure, or swelling.COVID‑19 vaccines have some adverse effects that are listed as common in the two or three days following vaccination which are usually mild and temporary. Causes
The rare simultaneous occurrence of thrombocytopenia (low blood platelets) with blood clots after vaccination raised the original concern about this condition. In many cases where acute thrombosis and thrombocytopenia have been found together after COVID‑19 vaccination, an antibody against platelet factor 4 has been identified. This phenomenon is mostly encountered in some people who have been administered heparin, but none of the reported cases had received heparin. More rarely, this phenomenon had previously been described as an autoimmune phenomenon in people who had not been exposed to heparin.
Alternative options as the directly acting oral anticoagulants (DOACs), argatroban, fondaparinux or danaparoid depending on the circumstances. Platelet transfusion is discouraged, as this too may aggravate thrombosis. UK guidelines by the British Society for Haematology recommend the administration of intravenous immunoglobulin (IVIG) to reduce levels of the pathogenic antibody. Low fibrinogen levels may require correction with fibrinogen concentrate or cryoprecipitate. Epidemiology
The Paul Ehrlich Institute has recorded 31 cerebral venous sinus thromboses (CVST) and nine deaths out of 2.7 million vaccinated in Germany with the AZD1222. On 2 April 2021, the UKs Medicines and Healthcare products Regulatory Agency reported 22 cases of CVST and a further eight cases of clotting problems both associated with a low level of blood platelets following a "rigorous review" of its Yellow Card reporting. The institute also reported finding no events of this type which occurred after vaccination with the Pfizer–BioNTech COVID‑19 vaccine. The EMA had earlier said that a link between certain very rare blood clots and the AstraZeneca vaccine is "not proven, but is possible".Observations in Germany of these rare events seemed to relate mostly women aged under 55. However, because Germany had previously restricted AZD1222 to under 65s, the population vaccinated there with AZD1222 is comparatively younger, and consequently contained a higher proportion of women taking the contraceptive pill. As CVSTs are more likely in women using hormonal contraceptives, this inherent risk factor may be an influence on the reported preponderance of women experiencing these events following vaccination.