Starting from day +1 after receiving the vaccine ChAdOx1 nCOV-19 (Oxford-Astrazeneca), a 48-year-old Caucasian woman reported progressive headache, back pain, moderate right lower limb pain, and disseminated ecchymosis that required hospitalization on day +18 for 7 days (S. Eugenio Hospital, Rome).

The clinical history included allergy to penicillin and an episode of thrombocytopenia in 2016. At the physical examinations, the patient appeared apyretic, with good hemodynamic compensation, absence of abnormal sounds at respiratory auscultation, soft abdomen and normal neurological objectivity, with a blood pressure of 214/125 mmHg. Laboratory tests showed a D-dimer value >10000 ng/mL and thrombocytopenia lower than 32000 platelets/μL. A pulmonary angio-CT showed thrombo-embolic filling defects affecting the pulmonary artery, in absence of any densitometric changes in the parenchyma. Venous echo-color doppler of the lower limbs showed absence of previous and/or concurrent deep venous obstructions. Low molecular weight heparin was administered.

On day +22, the patient required a transfer to the neurology intensive care unit to improve her management, as a significative intensification of headache, confusion, nausea, and vomiting emerged. The new therapeutic strategy included anti-hypertensive, and oral double (dabigatran 110 mg/die + rivaroxaban 30 mg/die) anti-coagulants in addition to i.v. methylprednisolone. In the following two days a drastic worsening of patient’s neurological symptoms including altered consciousness, strength deficit in the left side and right gaze deviation. An emergency skull CT documented massive right temporo-occipital intraparenchymal hemorrhage, extending to the ventricular system associated to midline shift; CT angiography investigating intra- and extra-cranial circulation showed thrombotic phenomena of the sigmoid transverse sinus and of the right internal jugular vein (Fig. 1A). The administration of Dabigatran antagonists and a decompressive craniectomy (day +23) was urgently performed. The patient remained comatose in intensive care for about 2 weeks, till day +16 after surgery (or day +39), when brain death was diagnosed.

Fig. 1: Thrombosis and preexisting myelodysplasia. Computed tomography angiography (CTA); A coronal view shows right internal jugular vein thrombosis (arrow), B axial view shows right transverse sinus thrombosis (arrow). A massive hemorrhagic focus is observed on right hemisphere (*). C Hematoxylin and eosin stain shows numerous degranulated megakaryocytes (arrows) (scale bar 100 µm). D Normal megakaryocyte characterized by large and abundant cytoplasm with more than 50 mature platelet granules (scale bar 5 µm). E Electron micrograph displays a megakaryocyte with few mature platelet granules (square) and numerous mitochondria (scale bar 3 µm). F A completely degranulated megakaryocyte (scale bar 5 µm). Table reports laboratory test results (full results in Supplementary Table 2). Full size image

Autoptic examination revealed a massive cerebral hemorrhage complicated by a purulent abscess involving the right fronto-temporo-parietal lobes, the nucleus of the right base, with midline shift and wedging of the cerebellar tonsils and an internal and external haemocephalus (Fig. 1B and Supplementary Fig. 1). Bilateral confluent foci of bronchopneumonia associated to a right apical pulmonary infarction of both lungs were also observed (Supplementary Fig. 2A, B). Postmortem analysis of bone marrow, including hematoxylin and eosin stain, immunohistochemistry, and transmission electron microscopy (TEM), showed focal megakaryocyte hyperplasia associated with morphological dysplastic changes. Abnormalities included non-lobulated or hypo-lobulated megakaryocytes, increase of cytoplasm, and separate or dark pycnotic nuclei (Fig. 1C–F and Fig. 2). Normal megakaryocytes (30–70 μm of diameter), characterized by large and hyperploid nuclei, accounted only 20% of the total population (Fig. 1B) and displayed more than 50 platelet granules (65,56 ± 8.67) (Fig. 1D). Conversely, the largest majority of megakaryocytes (~70%) displayed a significant impairment in the platelet granule formation (Fig. 1E, F), with degranulated cytoplasm and rare immature platelet granules (11.45 ± 4.14) (Fig. 1E). Five to ten percent of megakaryocytes were characterized by a complete impairment of platelet granules formation (Fig. 1F). TEM analysis of lung tissues further confirmed the frequent occurrence of vascular septic thrombi characterized by microvascular fibrin deposition (Fig. 3). Degenerated inflammatory cells, such as monocytes, were observed in several organized thrombi; vessels displayed no pericytes alteration. Signs of long standing petechiae were noted on the skin; hematoxylin–eosin staining reported a sclerosis of the dermis associated to nonspecific vasculitis infiltrated by CD3-positive T lymphocytes (Supplementary Fig. 3). All together, the ultrastructural data suggest the occurrence of a thrombocytopenia related to the impairment of megakaryocytes differentiation. Nevertheless, a paradoxical effect was observed in the lung with diffuse pulmonary thrombosis.

Fig. 2: Light and transmission electron microscopy of bone marrow. A Haematoxylin and eosin stain shows two large size degranulated megakaryocytes (asterisks) (scale bar 20 µm). B Toluidine blue stain displays a degranulated megakaryocytes with a large and segmented nucleus (asterisks) (scale bar 20 µm). C, D Degranulated megakaryocytes with fragmented nuclei (asterisks) (scale bar 10 µm). E Electron micrograph shows a megakaryocyte with rare immature/degenerated platelet granules. The cytoplasm included large amount of degenerating electrodense material (asterisk). The square highlights high magnification of an immature platelet granule (scale bar 5 µm). F A megakaryocyte with no/rare platelet granules (scale bar 5 µm). Full size image

Fig. 3: Histological analysis of lung thrombi. A–D Histological and electron microscopy analysis of lung tissues. Both PAS (A) and silver (B) staining show vascular thrombi (asterisks) in lung capillaries (scale bar 100 µm). C Electron micrograph shows vascular thrombi characterized by microvascular fibrin deposition (asterisks). The thrombi include degenerated monocytes (arrows) (scale bar 5 µm). D Image displays vascular thrombi with microvascular fibrin deposition (asterisks) and well-preserved pericytes (arrows) (scale bar 5 µm). Full size image

We also performed a WES genetic analysis on the patient’s PBMC. We studied more in details 64 genes involved in thrombocytopathies, complementopathies, and several platelets disfunction diseases [15, 16] and detected a total of 585 genetic variants. Introducing a cutoff at MAF 0.01, we selected 11 rare putative variants (1,88%): 1 out of these is a missense variant, 10 out of the total are intronic variants (Supplementary Table 1). According to the American College of Medical Genetics guidelines, these variants can be classified as benign and/or of unknown significance; also, the SERPINF2 missense variant emerged as benign and tolerated in all in silico prediction tools.

While the patient displayed several autoimmune autoantibodies (Supplementary Table 2), we failed to detect anti-PF4 antibodies, in contrast with most of the reported cases [11,12,13,14, 17], but in keeping with a similar case of ChAdOx1 nCOV-19 vaccine (Astrazeneca/Oxford) administration [18]. This suggests that in addition the immune thrombotic thrombocytopenia associated with antibodies that recognize PF4 and activate platelets through their Fcγ receptors, leading to autoimmune HIT [19, 20], other causes of thrombocytopenia, such as megakaryocyte dysplasia, could lead to potential life-threatening ADR. The underlying molecular events are not clear, even though platelets express ACE2, which can be triggered by SARS-CoV-2 binding to enhance thrombosis [21]; hence suggesting a stoichiometric relationship leading to the thrombotic event. Conversely, the vaccine administration has been associated to events of anti-PF4/polyanion antibodies production [22], but not in our specific case. We also detected the presence of NETosis, in keeping with its driving role in HIT [23], but only at a late stage and in the brain tissue, whilst the lung was depleted of neutrophils. Therefore, in keeping with the highly complex pattern of immune response to SARS-CoV-2, a sensible recommendation seems to be to avoid vaccination in thrombocytopenic patients and/or myelodysplastic patients or at least keep them under very strict control (https://www.gov.uk/government/publications/coronavirus-covid-19-vaccine-adverse-reactions/ coronavirus-vaccine-summary-of-yellow-card-reporting).