Treatment of vaccine-induced immune thrombotic thrombocytopenia (VITT)

Temporal changes in biomarkers of neutrophil extracellular traps and NET-promoting autoantibodies following adenovirus-vectored, mRNA, and recombinant protein COVID-19 vaccination

Neutrophil extracellular traps (NETs) play a role in innate pathogen defense and also trigger B-cell response by providing antigens. NETs have been linked to vaccine-induced thrombotic thrombocytopenia. We postulated a potential link between NET biomarkers, NET-promoting autoantibodies, and adverse events (AEs) after COVID-19 vaccine boosters. Healthy donors (HDs) who received ChAdOx1-S (A), mRNA-1273 (M), or recombinant protein (MVC-COV1901) vaccines at the National Taiwan University Hospital between 2021 and 2022 were recruited. We measured serial NET-associated biomarkers, citrullinated-histone3 (citH3), and myeloperoxidase (MPO)-DNA. Serum citH3 and MPO-DNA were significantly or numerically higher in HDs who reported AEs (n = 100, booster Day 0/Day 30, p = 0.01/p = 0.03 and p = 0.30/p = 0.35, respectively). We also observed a positive correlation between rash occurrence in online diaries and elevated citH3. A linear mixed model also revealed significantly higher citH3 levels in mRNA-1273/ChAdOx1-S recipients than MVC-COV1901 recipients. Significant positive correlations were observed between the ratios of anti-heparin platelet factor 4 and citH3 levels on Booster Day 0 and naïve and between the ratios of anti-NET IgM and citH3 on Booster Day 30/Day 0 in the AA-M and MM-M group, respectively. The increased levels of citH3/MPO-DNA accompanied by NET-promoting autoantibodies suggest a potential connection between mRNA-1273/ChAdOx1-S vaccines and cardiovascular complications. These findings provide insights for risk assessments of future vaccines.

Extensive splanchnic vein thrombosis after SARS-CoV-2 vaccination: A Vascular Liver Disease Group (VALDIG) initiative

BACKGROUND AND AIMS

Since the introduction of SARS-CoV-2 vaccines, several cases of vaccine-induced immune thrombocytopenia and thrombosis (VITT) have been described, especially cerebral vein thrombosis. We aimed to retrospectively collect all new cases of acute onset first or recurrent splanchnic vein thrombosis (SVT) following a recent SARS-CoV-2 vaccination within the Vascular Liver Disease Group network.

APPROACH AND RESULTS

New cases of SVT were identified from April 2021 to April 2022; follow-up was completed on December 31, 2022. Criteria to define VITT were derived from previous studies. Data from a pre-COVID cohort of patients with SVT (N=436) were used for comparison of clinical presentation, etiology, and outcome. Twenty-nine patients were identified with SVT occurring with a median of 11 days (range 2-76) after the first (48%), second (41%), or third (10%) vaccination (ChAdOx1 nCov-19 (n=12) or BNT162b2 (n=14), other (n=3) Only 2 patients(7%) fulfilled criteria for definite VITT. Twenty (69%) had SVT at multiple sites, including 4 (14%) with concomitant extra-abdominal thrombosis. Only 28% had an underlying prothrombotic condition, compared to 52% in the pre-COVID SVT cohort ( p =0.01). Five patients (17%) underwent bowel resection for mesenteric ischemia, compared with 3% in pre-COVID SVT ( p <0.001). Two patients died shortly after diagnosis (7%).

CONCLUSIONS

Although definite VITT was rare, in 72% of cases, no other cause for SVT could be identified following SARS-CoV-2 vaccination. These cases were different from patients with nonvaccine-related SVT, with lower incidence of prothrombotic conditions, higher rates of bowel ischemia, and poorer outcome. Although SVT after SARS-CoV-2 vaccination is rare in absolute terms, these data remain relevant considering ongoing revaccination programs.

Vaccine-Induced Immune Thrombotic Thrombocytopenia: Clinicopathologic Features and New Perspectives on Anti-PF4 Antibody-Mediated Disorders

INTRODUCTION

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare yet severe adverse complication first identified during the global vaccination effort against SARS-CoV-2 infection, predominantly observed following administration of the ChAdOx1-S (Oxford-AstraZeneca) and Ad26.CoV2.S (Johnson & Johnson/Janssen) adenoviral vector-based vaccines. Unlike other anti-platelet factor 4 (PF4) antibody-mediated disorders, such as heparin-induced thrombocytopenia (HIT), VITT arises with the development of platelet-activating anti-PF4 antibodies 4-42 days post-vaccination, typically featuring thrombocytopenia and thrombosis at unusual sites.

AIM

To explore the unique properties, pathogenic mechanisms, and long-term persistence of VITT antibodies in patients, in comparison with other anti-PF4 antibody-mediated disorders.

DISCUSSION

This review highlights the complexity of VITT as it differs in antibody behavior and clinical presentation from other anti-PF4-mediated disorders, including the high incidence rate of cerebral venous sinus thrombosis (CVST) and the persistence of anti-PF4 antibodies, necessitating a re-evaluation of long-term patient care strategies. The nature of VITT antibodies and the underlying mechanisms triggering their production remain largely unknown.

CONCLUSION

The rise in awareness and subsequent prompt recognition of VITT is paramount in reducing mortality. As vaccination campaigns continue, understanding the role of adenoviral vector-based vaccines in VITT antibody production is crucial, not only for its immediate clinical implications, but also for developing safer vaccines in the future.

Therapeutic strategies in FcγIIA receptor-dependent thrombosis and thromboinflammation as seen in heparin-induced thrombocytopenia (HIT) and vaccine-induced immune thrombocytopenia and thrombosis (VITT)

INTRODUCTION

Fcγ-receptors (FcγR) are membrane receptors expressed on a variety of immune cells, specialized in recognition of the Fc part of immunoglobulin G (IgG) antibodies. FcγRIIA-dependent platelet activation in platelet factor 4 (PF4) antibody-related disorders have gained major attention, when these antibodies were identified as the cause of the adverse vaccination event termed vaccine-induced immune thrombocytopenia and thrombosis (VITT) during the COVID-19 vaccination campaign. With the recognition of anti-PF4 antibodies as cause for severe spontaneous and sometimes recurrent thromboses independent of vaccination, their clinical relevance extended far beyond heparin-induced thrombocytopenia (HIT) and VITT.

AREAS COVERED

Patients developing these disorders show life-threatening thromboses, and the outcome is highly dependent on effective treatment. This narrative literature review summarizes treatment options for HIT and VITT that are currently available for clinical application and provides the perspective toward new developments.

EXPERT OPINION

Nearly all these novel approaches are based on in vitro, preclinical observations, or case reports with only limited implementation in clinical practice. The therapeutic potential of these approaches still needs to be proven in larger cohort studies to ensure treatment efficacy and long-term patient safety.

Anti-PF4 antibodies and their relationship with COVID infection

Detecting anti-PF4 antibodies remains the golden diagnostic method for heparin-induced thrombocytopenia (HIT) diagnosis with high sensitivity and specificity. Various lab tests detect anti-PF4 antibodies, including immunoassays and functional assays. Even with positive detection of the anti-PF4 antibody, several factors are involved in the result. The concept of anti-PF4 disorders was recently brought to light during the COVID pandemic since the development of vaccine-induced thrombotic thrombocytopenia (VITT) with the adenovirus-vectored-DNA vaccine during the pandemic. Circumstances that detect anti-PF4 antibodies are classified as anti-PF4 disorders, including VITT, autoimmune HIT and spontaneous HIT. Some studies showed a higher percentage of anti-PF4 antibody detection among the population infected by COVID-19 without heparin exposure and some supported the theory that the anti-PF4 antibodies were related to the disease severity. In this review article, we provide a brief review of anti-PF4 disorders and summarize the current studies of anti-PF4 antibodies and COVID-19 infection.

Hematology in the post-COVID era: spotlight on vaccine-induced immune thrombotic thrombocytopenia and a conceptual framework (the 4P's) for anti-PF4 diseases

INTRODUCTION

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a life-threatening prothrombotic disorder first identified following the introduction of adenoviral vector vaccines for COVID-19. The condition is characterized by anti-PF4 antibodies and clinically presents with thrombocytopenia and thrombosis often in unusual anatomical sites.

AREAS COVERED

In this review, we discuss the clinical presentation, diagnostic testing, and treatment of VITT. We also review VITT-like syndromes that have been described in patients without previous vaccination. We propose a conceptual framework for the mechanism of anti-PF4 diseases that includes sufficiently high levels of PF4, the presence of a Polyanion that can form immune complexes with PF4, a Pro-inflammatory milieu, and an immunological Predisposition - the 4Ps.

EXPERT OPINION

Significant progress has been made in understanding the characteristics of the VITT antibody and in testing methods that can confirm that diagnosis. Future work should be directed at understanding long-term outcomes, mechanisms of thrombosis, and individual risk factors for this rare but dangerous immune-thrombotic disease.

Reverse Engineering of a Pathogenic Antibody Reveals the Molecular Mechanism of Vaccine-Induced Immune Thrombotic Thrombocytopenia

The massive COVID-19 vaccine roll-out campaign illuminated a range of rare side effects, the most dangerous of which─vaccine-induced immune thrombotic thrombocytopenia (VITT)─is caused by adenoviral (Ad)-vectored vaccines. VITT occurrence had been linked to the production of pathogenic antibodies that recognize an endogenous chemokine, platelet factor 4 (PF4). Mass spectrometry (MS)-based evaluation of the ensemble of anti-PF4 antibodies obtained from a VITT patient's blood indicates that the major component is a monoclonal antibody. Structural characterization of this antibody reveals several unusual characteristics, such as the presence of an N-glycan in the Fab segment and high density of acidic amino acid residues in the complementarity-determining regions. A recombinant version of this antibody (RVT1) was generated by transient expression in mammalian cells based on the newly determined sequence. It captures the key properties of VITT antibodies such as their ability to activate platelets in a PF4 concentration-dependent fashion. Homology modeling of the Fab segment reveals a well-defined polyanionic paratope, and the docking studies indicate that the polycationic segment of PF4 readily accommodates two Fab segments, cross-linking the antibodies to yield polymerized immune complexes. Their existence was verified with native MS by detecting assemblies as large as (RVT1)3(PF4)2, pointing out at FcγRIIa-mediated platelet activation as the molecular mechanism underlying VITT clinical manifestations. In addition to the high PF4 affinity, RVT1 readily binds other polycationic targets, indicating a polyreactive nature of this antibody. This surprising promiscuity not only sheds light on VITT etiology but also opens up a range of opportunities to manage this pathology.

Autoimmune Heparin-Induced Thrombocytopenia

Autoimmune thrombocytopenia (aHIT) is a severe subtype of heparin-induced thrombocytopenia (HIT) with atypical clinical features caused by highly pathological IgG antibodies ("aHIT antibodies") that activate platelets even in the absence of heparin. The clinical features of aHIT include: the onset or worsening of thrombocytopenia despite stopping heparin ("delayed-onset HIT"), thrombocytopenia persistence despite stopping heparin ("persisting" or "refractory HIT"), or triggered by small amounts of heparin (heparin "flush" HIT), most cases of fondaparinux-induced HIT, and patients with unusually severe HIT (e.g., multi-site or microvascular thrombosis, overt disseminated intravascular coagulation [DIC]). Special treatment approaches are required. For example, unlike classic HIT, heparin cessation does not result in de-escalation of antibody-induced hemostasis activation, and thus high-dose intravenous immunoglobulin (IVIG) may be indicated to interrupt aHIT-induced platelet activation; therapeutic plasma exchange may be required if high-dose IVIG is ineffective. Also, aHIT patients are at risk for treatment failure with (activated partial thromboplastin time [APTT]-adjusted) direct thrombin inhibitor (DTI) therapy (argatroban, bivalirudin), either because of APTT confounding (where aHIT-associated DIC and resulting APTT prolongation lead to systematic underdosing/interruption of DTI therapy) or because DTI inhibits thrombin-induced protein C activation. Most HIT laboratories do not test for aHIT antibodies, contributing to aHIT under-recognition.

Laboratory Testing for Heparin-Induced Thrombocytopenia and Vaccine-Induced Immune Thrombotic Thrombocytopenia Antibodies: A Narrative Review

Heparin-induced thrombocytopenia (HIT) and vaccine-induced immune thrombotic thrombocytopenia (VITT) are highly prothrombotic (thrombosis frequency ≥50%). Both are caused by platelet-activating anti-platelet factor 4 (PF4) antibodies, forming PF4/IgG-containing immune complexes that engage platelet FcγIIa receptors, producing strong platelet activation. In HIT, heparin crosslinks several PF4 molecules, whereas in VITT, anti-PF4 antibodies alone crosslink PF4. Sufficient levels of circulating anti-PF4 antibodies are needed to create the pathogenic immune complexes on platelet surfaces; this explains why certain serum (plasma)-based assays are highly sensitive for detecting HIT/VITT antibodies. Accordingly, HIT and VITT are "clinical-pathological" disorders, that is, positive testing for such antibodies-together with a compatible clinical picture-is integral for diagnosis. Heparin (low concentrations) enhances HIT antibody-induced platelet activation, but platelet activation by VITT sera is usually inhibited by heparin. For both HIT and VITT, high sensitivity (>99% and >95%, respectively) characterizes PF4-dependent enzyme immunoassays (EIAs) and PF4-enhanced platelet activation assays; in contrast, certain rapid immunoassays have high sensitivity for HIT (>90-97%) but poor sensitivity (<25%) for VITT. HIT and VITT antibodies are directed at distinct sites on PF4: solid-phase EIAs and platelet activation assays are indifferent to these distinct antigen targets, but rapid immunoassays are not. We discuss a conceptual model where PF4 is viewed as a "globe," with the heparin-binding site the "equator"; in this model, HIT antibodies are primarily directed at antigen site(s) at the north and south "poles" of PF4 (formed when PF4 binds to heparin), whereas VITT antibodies recognize sites on the equator.

Long-term outcome in vaccine-induced immune thrombocytopenia and thrombosis

BACKGROUND

Rapid diagnosis and treatment has improved outcome of patients with vaccine-induced immune thrombocytopenia and thrombosis (VITT). However, after the acute episode, many questions on long-term management of VITT remained unanswered.

OBJECTIVES

To analyze, in patients with VITT, the long-term course of anti-platelet factor 4 (PF4) antibodies; clinical outcomes, including risk of recurrent thrombosis and/or thrombocytopenia; and the effects of new vaccinations.

METHODS

71 patients with serologically confirmed VITT in Germany were enrolled into a prospective longitudinal study and followed for a mean of 79 weeks from March 2021 to January 2023. The course of anti-PF4 antibodies was analyzed by consecutive anti-PF4/heparin immunoglobulin G enzyme-linked immunosorbent assay and PF4-enhanced platelet activation assay.

RESULTS

Platelet-activating anti-PF4 antibodies became undetectable in 62 of 71 patients (87.3%; 95% CI, 77.6%-93.2%). In 6 patients (8.5%), platelet-activating anti-PF4 antibodies persisted for >18 months. Five of 71 patients (7.0%) showed recurrent episodes of thrombocytopenia and/or thrombosis; in 4 of them (80.0%), alternative explanations beside VITT were present. After further COVID-19 vaccination with a messenger RNA vaccine, no reactivation of platelet-activating anti-PF4 antibodies or new thrombosis was observed. No adverse events occurred in our patients subsequently vaccinated against influenza, tick-borne encephalitis, varicella, tetanus, diphtheria, pertussis, and polio. No new thrombosis occurred in the 24 patients (33.8%) who developed symptomatic SARS-CoV-2 infection following recovery from acute VITT.

CONCLUSION

Once the acute episode of VITT has passed, patients appear to be at low risk for recurrent thrombosis and/or thrombocytopenia.

Platelet-neutrophil interaction in COVID-19 and vaccine-induced thrombotic thrombocytopenia

Coronavirus disease 2019 (COVID-19) is known to commonly induce a thrombotic diathesis, particularly in severely affected individuals. So far, this COVID-19-associated coagulopathy (CAC) has been partially explained by hyperactivated platelets as well as by the prothrombotic effects of neutrophil extracellular traps (NETs) released from neutrophils. However, precise insight into the bidirectional relationship between platelets and neutrophils in the pathophysiology of CAC still lags behind. Vaccine-induced thrombotic thrombocytopenia (VITT) is a rare autoimmune disorder caused by auto-antibody formation in response to immunization with adenoviral vector vaccines. VITT is associated with life-threatening thromboembolic events and thus, high fatality rates. Our concept of the thrombophilia observed in VITT is relatively new, hence a better understanding could help in the management of such patients with the potential to also prevent VITT. In this review we aim to summarize the current knowledge on platelet-neutrophil interplay in COVID-19 and VITT.

Vaccine-induced immune thrombotic thrombocytopenia: what do we know hitherto?

Vaccine-induced immune thrombotic thrombocytopenia (VITT), also known as thrombosis with thrombocytopenia syndrome, is a catastrophic and life-threatening reaction to coronavirus disease 2019 (COVID-19) vaccines, which occurs disproportionately in response to vaccination with non-replicating adenovirus vector (AV) vaccines. The mechanism of VITT is not well defined and it has not been resolved why cases of VITT are predominated by vaccination with AV vaccines. However, virtually all VITT patients have positive platelet-activating anti-platelet factor 4 (PF4) antibody titers. Subsequently, platelets are activated and depleted in an Fcγ-receptor IIa (FcγRIIa or CD32a)-dependent manner, but it is not clear why or how the anti-PF4 response is mounted. This review describes the pathogenesis of VITT and provides insight into possible mechanisms that prompt the formation of a PF4/polyanion complex, which drives VITT pathology, as an amalgam of current experimental data or hypotheses.

Hematologic adverse events reported after COVID-19 vaccination in the Philippines: A national database study

Vaccination is the most important strategy in preventing COVID-19. Vaccine efficacy and safety have been established in clinical trials but real-world data are useful to determine occurrence of adverse events in a population with heterogeneous characteristics. Knowledge on the hematologic events associated with different COVID-19 vaccines would be beneficial for patients as well as hematologists who oversee the care of these patients. This study aimed to determine the rates and outcomes of hematologic adverse events after COVID-19 vaccination in the Philippines. In this self-controlled case series, there were 268 individuals reported to have hematologic adverse events. Most received Comirnaty at 29.85%. Majority (62.31%) reported hematologic adverse events following the first dose of the vaccine. The overall event rate was 0.0182 per 10,000 vaccine doses; and lymphadenopathy was the most common hematologic adverse effect with a rate of 0.011 per 10,000 vaccine doses, followed by anemia at 0.0034 per 10,000 vaccine doses and thrombocytopenia at 0.0017 per 10,000 vaccine doses. Autoimmune cytopenias were also reported with an event rate of 0.0007 per 10,000 vaccine doses for ITP. One-hundred thirty two (49.25%) were fully recovered and 23.88% were recovering from hematologic adverse events as of the time of writing. The study showed a low rate of hematologic adverse events post COVID-19 vaccination with the seven different vaccine brands administered in the Philippines.

Molecular Mimicry of the Viral Spike in the SARS-CoV-2 Vaccine Possibly Triggers Transient Dysregulation of ACE2, Leading to Vascular and Coagulation Dysfunction Similar to SARS-CoV-2 Infection

The benefits of SARS-CoV-2 spike mRNA vaccines are well known, including a significant decline in COVID-19 morbidity and a decrease in the mortality rate of SARS-CoV-2 infected persons. However, pharmacovigilance studies have revealed the existence of rare cases of cardiovascular complications after mass vaccination using such formulations. Cases of high blood pressure have also been reported but were rarely documented under perfectly controlled medical supervision. The press release of these warning signals triggered a huge debate over COVID-19 vaccines' safety. Thereby, our attention was quickly focused on issues involving the risk of myocarditis, acute coronary syndrome, hypertension and thrombosis. Rare cases of undesirable post-vaccine pathophysiological phenomena should question us, especially when they occur in young subjects. They are more likely to occur with inappropriate use of mRNA vaccine (e.g., at the time when the immune response is already very active during a low-noise infection in the process of healing), leading to angiotensin II (Ang II) induced inflammation triggering tissue damage. Such harmful effects observed after the COVID-19 vaccine evoke a possible molecular mimicry of the viral spike transiently dysregulating angiotensin converting enzyme 2 (ACE2) function. Although the benefit/risk ratio of SARS-CoV-2 spike mRNA vaccine is very favorable, it seems reasonable to suggest medical surveillance to patients with a history of cardiovascular diseases who receive the COVID-19 vaccine.

Long VITT: A case report

Vaccine-induced immune thrombotic thrombocytopenia (VITT) has been described following adenovirus vector-based COVID-19 vaccines. This condition is associated with important morbidity and mortality following thrombosis related complications. Diagnosis is confirmed based on results of platelet factor 4 ELISA detecting anti-PF4 antibodies and of platelet-activation assay. Initial treatment strategy has been established but long-term management and follow up remain unclear. Most platelet-activation tests become negative after 12 weeks. We describe a case of VITT which can now be characterized as long VITT. The patient initially had a lower limb ischemia, pulmonary embolism and cerebral vein thrombosis. He was treated with prednisone, intravenous immunoglobulin, argatroban and had a lower limb revascularization surgery. Rivaroxaban was then initiated for the acute treatment and continued for the secondary prevention of recurrent events. The patient still demonstrates positive platelet-activation tests and thrombocytopenia after more than 18 months of follow-up. No recurrent thrombosis or bleeding event have occurred. He is not known for any relevant past medical history other than alcohol consumption and slight thrombocytopenia (130 × 10⁹/L since 2015). It is unclear if the ongoing and more important thrombocytopenia could be explained by the persistent platelet-activating anti-PF4 antibodies or the patient's habits. Managing long VITT is challenging considering uncertainty regarding risks and benefits of long-term anticoagulation and potential needs of additional treatment. Additional data is needed to offer optimal long-term management for this patient population. We suggest that long VITT diagnosis definition might include the persistence within patient serum/plasma of anti-PF4 platelet-activating antibodies with clinical manifestations (e.g., thrombocytopenia) for more than 3 months.

Investigation of Neurological Complications after COVID-19 Vaccination: Report of the Clinical Scenarios and Review of the Literature

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), broke out in 2019 and became a pandemic in 2020. Since then, vaccines have been approved to prevent severe illness. However, vaccines are associated with the risk of neurological complications ranging from mild to severe. Severe complications such as vaccine-induced immune thrombotic thrombocytopenia (VITT) associated with acute ischaemic stroke have been reported as rare complications post-COVID-19 vaccination. During the pandemic era, VITT evaluation is needed in cases with a history of vaccination within the last month prior to the event. Cerebral venous sinus thrombosis (CVST) should be suspected in patients following immunization with persistent headaches who are unresponsive to analgesics. In this article, we investigated neurological complications after COVID-19 vaccination and provided more subsequent related clinical studies of accurate diagnosis, pathophysiological mechanisms, incidence, outcome, and management.

Hematological Questions in Personalized Management of COVID-19 Vaccination

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been causing a worldwide pandemic since 2019. Many vaccines have been manufactured and have shown promising results in reducing disease morbidity and mortality. However, a variety of vaccine-related adverse effects, including hematological events, have been reported, such as thromboembolic events, thrombocytopenia, and bleeding. Moreover, a new syndrome, vaccine-induced immune thrombotic thrombocytopenia, following vaccination against COVID-19 has been recognized. These hematologic side effects have also raised concerns about SARS-CoV-2 vaccination in patients with preexisting hematologic conditions. Patients with hematological tumors are at a higher risk of severe SARS-CoV-2 infection, and the efficacy and safety of vaccination in this group remain uncertain and have raised attention. In this review, we discuss the hematological events following COVID-19 vaccination and vaccination in patients with hematological disorders.

Vaccine-induced immune thrombotic thrombocytopenia (VITT) after SARS-CoV-2 vaccination: Two cases from Germany with unusual presentation

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare clinical condition that has emerged during the mass immunization against SARS-CoV-2. Reports indicate that VITT may also be induced by other vaccines, such as the human papillomavirus vaccine, or occur independently of vaccination. Its recognition requires a high index of suspicion, especially in patients presenting with thrombocytopenia and thrombosis several days after vaccination with an adenoviral vector-based vaccine against SARS-CoV-2. Bleeding manifestations do not exclude VITT, as initially assumed. It is of great importance to perform the appropriate diagnostic tests early in the course of the disease, as false-negative results may occur and many aspects of VITT are not fully understood. These two cases from Germany demonstrate unusual presentations of VITT.

Unique features of vaccine-induced immune thrombotic thrombocytopenia; a new anti-platelet factor 4 antibody-mediated disorder

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a highly prothrombotic disorder caused by anti-PF4 antibodies that activate platelets and neutrophils, leading to thrombosis. Heparin-induced thrombocytopenia (HIT) is a related anti-PF4 mediated disorder, with similar pathophysiology and clinical manifestations but different triggers (i.e., heparin vs adenoviral vector vaccine). Clinically, both HIT and VITT typically present with thrombocytopenia and thrombosis, although the risk of thrombosis is significantly higher in VITT, and the thromboses occur in unusual anatomical sites (e.g., cerebral venous sinus thrombosis and hepatic vein thrombosis). The diagnostic accuracy of available laboratory testing differs between HIT and VITT; for VITT, ELISAs have better specificity compared to HIT and platelet activation assays require the addition of PF4. Treatment of VITT and HIT is anticoagulation non-heparin anticoagulants; however, heparin may be considered for VITT if no other option is available.

Pilot Findings on SARS-CoV-2 Vaccine-Induced Pituitary Diseases: A Mini Review from Diagnosis to Pathophysiology

Since the emergence of the COVID-19 pandemic at the end of 2019, a massive vaccination campaign has been undertaken rapidly and worldwide. Like other vaccines, the COVID-19 vaccine is not devoid of side effects. Typically, the adverse side effects of vaccination include transient headache, fever, and myalgia. Endocrine organs are also affected by adverse effects. The major SARS-CoV-2 vaccine-associated endocrinopathies reported since the beginning of the vaccination campaign are thyroid and pancreas disorders. SARS-CoV-2 vaccine-induced pituitary diseases have become more frequently described in the literature. We searched PubMed/MEDLINE for commentaries, case reports, and case series articles reporting pituitary disorders following SARS-CoV-2 vaccination. The search was reiterated until September 2022, in which eight case reports were found. In all the cases, there were no personal or familial history of pituitary disease described. All the patients described had no previous SARS-CoV-2 infection prior to the vaccination episode. Regarding the type of vaccines administered, 50% of the patients received (BNT162b2; Pfizer-BioNTech) and 50% received (ChAdOx1 nCov-19; AstraZeneca). In five cases, the pituitary disorder developed after the first dose of the corresponding vaccine. Regarding the types of pituitary disorder, five were hypophysitis (variable clinical aspects ranging from pituitary lesion to pituitary stalk thickness) and three were pituitary apoplexy. The time period between vaccination and pituitary disorder ranged from one to seven days. Depending on each case's follow-up time, a complete remission was obtained in all the apoplexy cases but in only three patients with hypophysitis (persistence of the central diabetes insipidus). Both quantity and quality of the published data about pituitary inconveniences after COVID-19 vaccination are limited. Pituitary disorders, unlike thyroid disorders, occur very quickly after COVID-19 vaccination (less than seven days for pituitary disorders versus two months for thyroid disease). This is partially explained by the ease of reaching the pituitary, which is a small gland. Therefore, this gland is rapidly overspread, which explains the speed of onset of pituitary symptoms (especially ADH deficiency which is a rapid onset deficit with evocative symptoms). Accordingly, these pilot findings offer clinicians a future direction to be vigilant for possible pituitary adverse effects of vaccination. This will allow them to accurately orient patients for medical assistance when they present with remarkable symptoms, such as asthenia, polyuro-polydipsia, or severe headache, following a COVID-19 vaccination.

Vaccine-induced immune thrombotic thrombocytopenia

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is primarily a complication of adenoviral vector-based covid-19 vaccination. In VITT, thrombocytopenia and thrombosis mediated by anti-platelet factor 4 (PF4) antibodies can be severe, often characterized by thrombosis at unusual sites such as the cerebral venous sinus and splanchnic circulation. Like in heparin-induced thrombocytopenia (HIT) and spontaneous HIT, VITT antibodies recognize PF4-polyanion complexes and activate PF4-treated platelets but additionally bind to un-complexed PF4, a critical finding that could be leveraged for more specific detection of VITT. Intravenous immunoglobulin and non-heparin-based anticoagulation remain the mainstay of treatment. Second dose/boosters of mRNA covid-19 vaccines appear safe in patients with adenoviral vector-associated VITT. Emerging data is consistent with the possibility that ultra-rare cases of VITT may be seen in the setting of mRNA and virus-like particle (VLP) technology-based vaccinations and until more data is available, it is prudent to consider VITT in the differential diagnosis of all post-vaccine thrombosis and thrombocytopenia reactions.