An observational study to identify the prevalence of thrombocytopenia and anti-PF4/polyanion antibodies in Norwegian health care workers after COVID-19 vaccination

Neurovascular Adverse Effects of Sars-Cov-2 Vaccination

The global deployment of SARS-CoV-2 vaccines has been pivotal in curbing the COVID-19 pandemic, reducing morbidity and mortality associated with the virus. While most of these vaccines have demonstrated high efficacy and overall safety, emerging reports have highlighted potential neurovascular adverse effects, albeit uncommon, associated with these vaccinations. This review aims to assess and summarize the current knowledge on the neurovascular complications arising post-SARS-CoV-2 vaccination. We conducted an extensive literature review, focusing on clinical studies and case reports to identify reported neurovascular events, such as ischemic stroke, cerebral sinus venous thrombosis, intracerebral hemorrhage, pituitary apoplexy and primary CNS angiitis Despite the relative rarity of these events, their impact on affected individuals underscores the importance of ongoing surveillance, early detection, and management strategies. We aim to provide healthcare professionals with the latest evidence on neurovascular adverse effects, facilitating informed decision-making in the context of SARS-CoV-2 vaccination programs. Furthermore, we highlight areas requiring further research to understand the pathophysiology of these adverse events better and to develop targeted prevention and treatment strategies.

Thrombosis with thrombocytopenia syndrome (TTS) and vaccine-induced immune thrombocytopenia and thrombosis (VITT): Brighton Collaboration case definitions and guidelines for data collection, analysis, and presentation of immunisation safety data

This is a revision of the online November 2021 Brighton thrombosis with thrombocytopenia syndrome (TTS) case definition and a new Brighton Collaboration case definition for vaccine-induced immune thrombocytopenia and thrombosis (VITT). These case definitions are intended for use in clinical trials and post-licensure pharmacovigilance activities to facilitate safety data comparability across multiple settings. They are not intended to guide clinical management. The case definitions were developed by a group of subject matter and Brighton Collaboration process experts as part of the Coalition for Epidemic Preparedness Innovations (CEPI)-funded Safety Platform for Evaluation of vACcines (SPEAC). The case definitions, each with defined levels of diagnostic certainty, are based on relevant published evidence and expert consensus and are accompanied by specific guidelines for TTS and VITT data collection and analysis. The document underwent peer review by a reference group of vaccine safety stakeholders and haematology experts to ensure case definition useability, applicability and scientific integrity.

Transient Autoreactive PF4 and Antiphospholipid Antibodies in COVID-19 Vaccine Recipients

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare autoimmune condition associated with recombinant adenovirus (rAV)-based COVID-19 vaccines. It is thought to arise from autoantibodies targeting platelet factor 4 (aPF4), triggered by vaccine-induced inflammation and the formation of neo-antigenic complexes between PF4 and the rAV vector. To investigate the specific induction of aPF4 by rAV-based vaccines, we examined sera from rAV vaccine recipients (AZD1222, AD26.COV2.S) and messenger RNA (mRNA) based (mRNA-1273, BNT162b2) COVID-19 vaccine recipients. We compared the antibody fold change (FC) for aPF4 and for antiphospholipid antibodies (aPL) of rAV to mRNA vaccine recipients. We combined two biobanks of Dutch healthcare workers and matched rAV-vaccinated individuals to mRNA-vaccinated controls, based on age, sex and prior history of COVID-19 (AZD1222: 37, Ad26.COV2.S: 35, mRNA-1273: 47, BNT162b2: 26). We found no significant differences in aPF4 FCs after the first (0.99 vs. 1.08, mean difference (MD) = -0.11 (95% CI -0.23 to 0.057)) and second doses of AZD1222 (0.99 vs. 1.10, MD = -0.11 (95% CI -0.31 to 0.10)) and after a single dose of Ad26.COV2.S compared to mRNA-based vaccines (1.01 vs. 0.99, MD = 0.026 (95% CI -0.13 to 0.18)). The mean FCs for the aPL in rAV-based vaccine recipients were similar to those in mRNA-based vaccines. No correlation was observed between post-vaccination aPF4 levels and vaccine type (mean aPF difference -0.070 (95% CI -0.14 to 0.002) mRNA vs. rAV). In summary, our study indicates that rAV and mRNA-based COVID-19 vaccines do not substantially elevate aPF4 levels in healthy individuals.

COVID-19 vaccine-induced immune thrombotic thrombocytopenia: pathophysiology and diagnosis

Coronavirus disease-19 (COVID-19) vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare but serious clinical condition with high mortality rate in apparently healthy individuals without noticeable risk factors. VITT typically arises due to the administration of vaccines that possess recombinant adenoviral vectors, including ChAdOx1 nCov-19 (AstraZeneca) and Ad26 COV2.S (Johnson & Johnson/Janssen). Thrombosis frequently occurs at atypical sites, such as the cerebral or splanchnic circulations, in this particular pathological state. Similar to heparin-induced thrombotic thrombocytopenia (HITT), it seems that the cause of VITT is the misdirection of anti-platelet factor 4 antibodies (anti-PF4 Abs), an ancient antimicrobial mechanism. Anti-PF4 Abs in patients with VITT activates the coagulation system, leading to thrombosis. This process occurs through the stimulation of platelets (Plts) and neutrophils and subsequently release of neutrophil extracellular traps (NETs). Due to the potentially fatal consequences of VITT, early diagnosis is mandatory. In addition to thrombocytopenia, thrombosis, and the presence of anti-PF4 Abs, the day of symptoms onset and the elevation of D-dimer are also required for definitive diagnosis of VITT. The absence of one or more criteria can result in the exclusion of definitive VITT and lead to the diagnosis of probable, possible, or unlikely VITT.

The clinicopathological features of thrombosis with thrombocytopenia syndrome following ChAdOx1-S (AZD1222) vaccination and case outcomes in Australia: a population-based study

Background

Thrombosis with thrombocytopenia syndrome (TTS) associated with viral vector COVID-19 vaccines, including ChAdOx1-S (AstraZeneca AZD1222) vaccine, can result in significant morbidity and mortality. We report the clinicopathological features of TTS following ChAdOx1-S vaccination and summarise the case outcomes in Australia.

Methods

In this cohort study, patients diagnosed with TTS in Australia between 23 March and 31 December 2021 were identified according to predefined criteria. Cases were included if they met the Therapeutic Goods Administration (TGA) probable and confirmed case definitions and were reclassified using Centres for Disease Control and Prevention (CDC) definition for analysis. Data were collected on patient baseline characteristics, clinicopathological features, risk factors, treatment and outcomes.

Findings

A total of 170 TTS cases were identified, with most occurring after the first dose (87%) of ChAdOx1-S. The median time to symptom onset after vaccination and symptom onset to admission was 11 and 2 days respectively. The median age of cases was 66 years (interquartile range 55-74). All except two patients received therapeutic anticoagulation and 66% received intravenous immunoglobulin. Overall, 85.3% of cases were discharged home after a median hospitalisation of 6 days, 9.4% required ongoing rehabilitation and 5.3% died. Eight deaths were related to TTS, with another dying from an unrelated condition while receiving treatment for TTS. Deaths occurred more commonly in those classified as Tier 1 according to the CDC definition and were associated with more severe thrombocytopenia and disease-related haemorrhage.

Interpretation

TTS, while rare, can be severe and have catastrophic outcomes in some individuals. In Australia, the mortality rate was low compared to that reported in other high-income countries. Almost all received therapeutic anticoagulation with no bleeding complications and were successfully discharged. This emphasises the importance of community education and an established pathway for early recognition, diagnosis and treatment of TTS.

Funding

Australian Commonwealth Department of Health and Aged Care. H.A Tran, N. Wood, J. Buttery, N.W. Crawford, S.D. Chunilal, V.M. Chen are supported by Medical Research Future Funds (MRFF) grant ID 2015305.

Blood Coagulation and Thrombotic Disorders following SARS-CoV-2 Infection and COVID-19 Vaccination

Although abundant data confirm the efficacy and safety profile of the developed vaccines against COVID-19, there are still some concerns regarding vaccination in high-risk populations. This is especially valid for patients susceptible to thrombotic or bleeding events and hesitant people due to the fear of thrombotic incidents following vaccination. This narrative review focuses on various inherited and acquired thrombotic and coagulation disorders and the possible pathophysiologic mechanisms interacting with the coagulation system during immunization in view of the currently available safety data regarding COVID-19 vaccines. Inherited blood coagulation disorders and inherited thrombotic disorders in the light of COVID-19, as well as blood coagulation and thrombotic disorders and bleeding complications following COVID-19 vaccines, along with the possible pathogenesis hypotheses, therapeutic interventions, and imaging for diagnosing are discussed in detail. Lastly, the lack of causality between the bleeding and thrombotic events and COVID-19 vaccines is debated, but still emphasizes the importance of vaccination against COVID-19, outweighing the minimal risk of potential rare adverse events associated with coagulation.

Incidence of anti-platelet factor4/polyanionic antibodies, thrombocytopenia, and thrombosis after COVID-19 vaccination with ChAdOx1 nCoV-19 in Thais

BACKGROUND

The prevalence of anti-platelet factor 4 (PF4)/polyanionic antibodies occurring after vaccination with ChAdOx1 nCoV-19 is low. Most of these antibodies are not associated with vaccine-induced thrombotic thrombocytopenia. It remains unknown whether these antibodies are preexisting or occur as a result of vaccination. In this study, we demonstrated the incidence of anti-PF4/polyanionic antibodies, thrombocytopenia, and thrombosis after vaccination with ChAdOx1 nCoV-19 in a large cohort of Thais.

METHODS

We conducted a prospective study in a cohort of health care workers and members of the general population who received COVID-19 vaccination with ChAdOx1 nCoV-19. Blood collection for complete blood count, D-dimer, and anti-PF4/polyanionic antibodies was performed before vaccination (day 0), day 10, and day 28 after vaccination. Anti-PF4/polyanionic antibodies were detected using enzyme-link immunosorbent assay (ELISA). Functional assay was performed for all positive ELISA tests.

RESULTS

A total of 720 participants were included in the study. 214 participants received both the first and second doses, 91 participants received only the first, 51 received only the second, and 364 received the third booster dose of ChAdOx1 nCoV-19. Median age was 42 years (IQR, 34-53). 67% of participants were female. Three participants developed seroconversion, yielding an incidence of vaccination-induced anti-PF4/polyanionic antibodies of 0.42% (95% confidence interval 0.08, 1.23). Fourteen (1.9%) participants had preexisting anti-PF4/polyanionic antibodies before the vaccination but their optical density of anti-PF4/polyanionic antibodies did not significantly increase over time. None of the anti-PF4/polyanionic positive sera induced platelet aggregation. Abnormal D-dimer levels following vaccination were not different among the positive and negative anti-PF4/polyanionic groups (11.8% vs. 13.2%, p = 0.86). Thrombocytopenia occurred in one person with negative anti-PF4/polyanionic antibodies. No clinical thrombosis or bleeding occurred.

CONCLUSION

We found a low incidence of seroconversion of anti-PF4/polyanionic antibodies after vaccination with ChAdOx1 nCoV-19 in Thais. Most of the anti-PF4/polyanionic antibodies were preexisting and did not significantly increase after vaccination with ChAdOx1 nCoV-19. Following vaccination, some participants with anti-PF4/polyanionic antibodies had elevated D-dimer levels, while only one developed thrombocytopenia and no thrombotic events were observed.

Serious neurological adverse events following immunization against SARS-CoV-2: a narrative review of the literature

Amid the coronavirus disease 2019 (COVID-19) pandemic, massive immunization campaigns became the most promising public health measure. During clinical trials, certain neurological adverse effects following immunization (AEFIs) were observed; however, acceptable safety profiles lead to emergency authorization for the distribution and use of the vaccines. To contribute to pharmacovigilance and lessen the potential negative impact that vaccine hesitancy would have on immunization programs, we conducted a review of the scientific literature concerning the epidemiological data, clinical presentation, and potential mechanisms of these neurological AEFIs. There is some epidemiological evidence linking COVID-19 vaccines to cerebral venous sinus thrombosis, arterial ischemic stroke, convulsive disorder, Guillain-Barré syndrome, facial nerve palsy, and other neurological conditions. Cerebral venous sinus thrombosis has been associated with a thrombotic thrombocytopenia induced by the vaccine, similar to that induced by heparin, which suggests similar pathogenic mechanisms (likely involving antibodies against platelet factor 4, a chemokine released from activated platelets). Arterial ischemic stroke is another thrombotic condition observed among some COVID-19 vaccine recipients. Vaccine-induced convulsive disorder might be the result of structural abnormalities potentially caused by the vaccine or autoimmune mechanisms. Guillain-Barré syndrome and facial nerve palsy may also be linked to the immunization event, possibly due to immune mechanisms such as uncontrolled cytokine release, autoantibody production, or bystander effect. However, these events are mostly uncommon and the evidence for the association with the vaccine is not conclusive. Furthermore, the potential pathophysiological mechanisms remain largely unknown. Nevertheless, neurological AEFIs can be serious, life-threatening or even fatal. In sum, COVID-19 vaccines are generally safe and the risk of neurological AEFIs does not outweigh the benefits of immunization. However, early diagnosis and treatment of neurological AEFIs are of utmost importance, and both health professionals and the public should be aware of these conditions.

Longitudinal Profiles of Anti-Platelet Factor 4 Antibodies in Thai People Who Received ChAdOx1 nCoV-19 Vaccination

Anti-platelet factor 4 (anti-PF4) antibodies were identified as pathogenic antibodies for vaccine-induced immune thrombocytopenia and thrombosis (VITT) in subjects receiving ChAdOx1 nCoV-19 vaccinations. We performed a prospective cohort study to determine the prevalence of anti-PF4 and the effect of the ChAdOx1 nCoV-19 vaccine on anti-PF4 in healthy Thai subjects. Anti-PF4 antibodies were measured before and four weeks after receiving the first vaccination. Participants with detectable antibodies were scheduled for repeat anti-PF4 analysis at 12 weeks after the second vaccination. Of 396 participants, ten participants (2.53%; 95% confidence interval [CI], 1.22-4.59) were positive for anti-PF4 before receiving vaccinations. Twelve people (3.03%; 95% CI, 1.58-5.23) had detectable anti-PF4 after the first vaccination. There was no difference in the optical density (OD) values of anti-PF4 antibodies when comparisons were made between pre-vaccination and four weeks after the first vaccination (p = 0.0779). There was also no significant difference in OD values in participants with detectable antibodies. No subjects experienced thrombotic complications. Pain at the injection site was associated with an increased risk of being anti-PF4 positive at an odds ratio of 3.44 (95% CI, 1.06-11.18). To conclude, the prevalence of anti-PF4 was low in Thais and did not significantly change over time.

Head-to-head comparison of four COVID-19 vaccines on platelet activation, coagulation and inflammation. The TREASURE study

INTRODUCTION

Studies exploring alterations in blood coagulation and platelet activation induced by COVID-19 vaccines are not concordant. We aimed to assess the impact of four COVID-19 vaccines on platelet activation, coagulation, and inflammation considering also the immunization dose and the history of SARS-CoV-2 infection.

METHODS

TREASURE study enrolled 368 consecutive subjects (161 receiving viral vector vaccines -ChAdOx1-S/Vaxzevria or Janssen- and 207 receiving mRNA vaccines -Comirnaty/Pfizer-BioNTech or Spikevax/Moderna). Blood was collected the day before and 8 ± 2 days after the vaccination. Platelet activation markers (P-selectin, aGPIIbIIIa and Tissue Factor expression; number of platelet-monocyte and -granulocyte aggregates) and microvesicle release were analyzed by flow cytometry. Platelet thrombin generation (TG) capacity was measured using the Calibrated Automated Thrombogram. Plasma coagulation and inflammation markers and immune response were evaluated by ELISA.

RESULTS

Vaccination did not induce platelet activation and microvesicle release. IL-6 and CRP levels (+30%), D-dimer, fibrinogen and F₁₊₂ (+13%, +3.7%, +4.3%, respectively) but not TAT levels significantly increased upon immunization with all four vaccines, with no difference among them and between first and second dose. An overall minor post-vaccination reduction of aPC, TM and TFPI, all possibly related to endothelial function, was observed. No anti-PF4 seroconversion was observed.

CONCLUSION

This study showed that the four COVID-19 vaccines administered to a large population sample induce a transient inflammatory response, with no onset of platelet activation. The minor changes in clotting activation and endothelial function might be potentially involved at a population level in explaining the very rare venous thromboembolic complications of COVID-19 vaccination.

Platelet Activation and Cytokine Release of Interleukin-8 and Interferon-Gamma-Induced Protein 10 after ChAdOx1 nCoV-19 Coronavirus Vaccine Injection

Coronavirus disease 2019 (COVID-19) vaccines are associated with serious thromboembolic or thrombocytopenic events including vaccine-induced immune thrombocytopenia and thrombosis and immune thrombocytopenia, particularly AZD1222/ChAdOx1. According to the proposed mechanism, COVID-19 vaccines stimulate inflammation and platelet activation. In this study, we analyzed the role of AZD1222/ChAdOx1 vaccines in the activation of platelets and the release of anti-PF4 antibodies and inflammatory cytokines in a cohort of healthy donors without vaccine-induced immune thrombotic thrombocytopenia (VITT). Forty-eight healthy volunteers were enrolled in this study. Blood samples were collected from peripheral blood at three time points: before vaccination and 1 and 7 days after vaccination. Compared with the prevaccination data, a decrease in the leukocyte and platelet counts was observed 1 day after vaccination, which recovered 7 days after injection. The percentage of activated GPIIb/IIIa complex (PAC-1) under high ADP or thrombin receptor-activating peptide stimulation increased 1 day after vaccination. Furthermore, interluekin-8 (IL-8) and interferon-gamma-induced protein 10 (IP-10) increased significantly. Additionally, platelet activation and inflammation, with the release of cytokines, were observed; however, none of the individuals developed VITT. Mild thrombocytopenia with platelet activation and inflammation with an elevation of IL-8 and IP-10 were observed after AZ vaccination.

From Co-Infections to Autoimmune Disease via Hyperactivated Innate Immunity: COVID-19 Autoimmune Coagulopathies, Autoimmune Myocarditis and Multisystem Inflammatory Syndrome in Children

Neutrophilia and the production of neutrophil extracellular traps (NETs) are two of many measures of increased inflammation in severe COVID-19 that also accompany its autoimmune complications, including coagulopathies, myocarditis and multisystem inflammatory syndrome in children (MIS-C). This paper integrates currently disparate measures of innate hyperactivation in severe COVID-19 and its autoimmune complications, and relates these to SARS-CoV-2 activation of innate immunity. Aggregated data include activation of Toll-like receptors (TLRs), nucleotide-binding oligomerization domain (NOD) receptors, NOD leucine-rich repeat and pyrin-domain-containing receptors (NLRPs), retinoic acid-inducible gene I (RIG-I) and melanoma-differentiation-associated gene 5 (MDA-5). SARS-CoV-2 mainly activates the virus-associated innate receptors TLR3, TLR7, TLR8, NLRP3, RIG-1 and MDA-5. Severe COVID-19, however, is characterized by additional activation of TLR1, TLR2, TLR4, TLR5, TLR6, NOD1 and NOD2, which are primarily responsive to bacterial antigens. The innate activation patterns in autoimmune coagulopathies, myocarditis and Kawasaki disease, or MIS-C, mimic those of severe COVID-19 rather than SARS-CoV-2 alone suggesting that autoimmunity follows combined SARS-CoV-2-bacterial infections. Viral and bacterial receptors are known to synergize to produce the increased inflammation required to support autoimmune disease pathology. Additional studies demonstrate that anti-bacterial antibodies are also required to account for known autoantigen targets in COVID-19 autoimmune complications.

Heparin-Induced Thrombotic Thrombocytopenia (HITT) and Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT): Similar but Different

Heparin-induced thrombocytopenia (HIT) represents an autoimmune process whereby antibodies are formed against heparin in complex with platelet factor 4 (PF4) after heparin administration. These antibodies can be detected by a variety of immunological assays, including ELISA (enzyme-linked immunosorbent assay) and by chemiluminescence on the AcuStar instrument. However, pathological HIT antibodies are those that activate platelets in a platelet activation assay and cause thrombosis in vivo. We would tend to call this condition heparin-induced thrombotic thrombocytopenia (HITT), although some workers instead use the truncated abbreviation HIT. Vaccine-induced (immune) thrombotic thrombocytopenia (VITT) instead reflects an autoimmune process whereby antibodies are formed against PF4 after administration of a vaccine, most notably adenovirus-based vaccines directed against COVID-19 (coronavirus disease 2019). Although both VITT and HITT reflect similar pathological processes, they have different origins and are detected in different ways. Most notable is that anti-PF4 antibodies in VITT can only be detected immunologically by ELISA assays, tending to be negative in rapid assays such as that using the AcuStar. Moreover, functional platelet activation assays otherwise used for HITT may need to be modified to detect platelet activation in VITT.

SARS-CoV-2 vaccines are not associated with hypercoagulability in apparently healthy people

Background

SARS-CoV-2 adenoviral vector DNA vaccines have been linked to the rare but serious thrombotic postvaccine complication vaccine-induced immune thrombotic thrombocytopenia. This has raised concerns regarding the possibility of increased thrombotic risk after any SARS-CoV-2 vaccines.

Objectives

To investigate whether SARS-CoV-2 vaccines cause coagulation activation leading to a hypercoagulable state.

Methods

This observational study included 567 health care personnel; 521 were recruited after the first dose of adenoviral vector ChAdOx1-S (Vaxzevria, AstraZeneca) vaccine and 46 were recruited prospectively before vaccination with a messenger RNA (mRNA) vaccine, either Spikevax (Moderna, n = 38) or Comirnaty (Pfizer-BioNTech, n = 8). In the mRNA group, samples were acquired before and 1 to 2 weeks after vaccination. In addition to the prevaccination samples, 56 unvaccinated blood donors were recruited as controls (total n = 102). Thrombin generation, D-dimer levels, and free tissue factor pathway inhibitor (TFPI) levels were analyzed.

Results

No participant experienced thrombosis, vaccine-induced immune thrombotic thrombocytopenia, or thrombocytopenia (platelet count <100 × 10⁹/L) 1 week to 1 month postvaccination. There was no increase in thrombin generation, D-dimer level, or TFPI level in the ChAdOx1-S vaccine group compared with controls or after the mRNA vaccines compared with baseline values. Eleven of 513 (2.1%) participants vaccinated with ChAdOx1-S had anti-PF4/polyanion antibodies without a concomitant increase in thrombin generation.

Conclusion

In this study, SARS-CoV-2 vaccines were not associated with thrombosis, thrombocytopenia, increased thrombin generation, D-dimer levels, or TFPI levels compared with baseline or unvaccinated controls. These findings argue against the subclinical activation of coagulation post-COVID-19 vaccination.

Influenza vaccination features revealed by a single-cell transcriptome atlas

Emerging and re-emerging viruses like influenza virus pose a continuous global public health threat. Vaccines are one of the most effective public health strategies for controlling infectious diseases. However, little is known about the immunological features of vaccination at the single-cell resolution, including for influenza vaccination. Here, we report the single-cell transcriptome atlas of longitudinally collected peripheral blood mononuclear cells (PBMCs) in individuals immunized with an inactivated influenza vaccine. Overall, vaccination with the influenza vaccine only had a small impact on the composition of peripheral immune cells, but elicited global transcriptional changes in multiple immune cell subsets. In plasma and B cell subsets, transcriptomic changes, which were mostly involved in antibody production as well as B cell activation and differentiation, were observed after influenza vaccinations. In influenza-vaccinated individuals, we found a reduction in multiple biological processes (e.g., interferon response, inflammatory response, HLA-I/II molecules, cellular apoptosis, migration, and cytotoxicity, etc.,) 7 days postvaccination in multiple immune cell subsets. However, 14 days postvaccination, these levels returned to similar levels observed in prevaccination samples. Additionally, we did not observe significant upregulation of pro-inflammatory response genes and key thrombosis-related genes in influenza-vaccinated individuals. Taken together, we report a cell atlas of the peripheral immune response to influenza vaccination and provide a resource for understanding the immunological response mechanisms of influenza vaccination.

Vaccine associated benign headache and cutaneous hemorrhage after ChAdOx1 nCoV-19 vaccine: A cohort study

OBJECTIVES

Fatal complications have occurred after vaccination with ChAdOx1 nCoV-19, a vaccine against Covid-19. Vaccine-induced immune thrombotic thrombocytopenia (VITT) with severe outcome is characterized by venous thrombosis, predominantly in cerebral veins, thrombocytopenia and anti-PF4/polyanion antibodies. Prolonged headaches and cutaneous hemorrhages, frequently observed after the ChAdOx1 nCoV-19 vaccine, have therefore caused anxiety among vaccinees. We investigated whether these symptoms represent a mild form of VITT, with a potential for aggravation, e.g. in case of a second vaccination dose, or a different entity of vaccine complications MATERIALS AND METHODS: We included previously healthy individuals who had a combination of headache and spontaneous severe cutaneous hemorrhages emerging after the 1^st dose of the ChAdOx1 nCoV-19 vaccine. Twelve individuals were found to meet the inclusion criteria, and a phone interview, cerebral MRI, assessment of platelet counts, anti PF4/polyanion antibodies and other laboratory tests were performed.

RESULTS

None of the symptomatic vaccinees had cerebral vein thrombosis, hemorrhage or other pathology on MRI. Platelet counts were within normal range and no anti-PF4/polyanion platelet activating antibodies were found. Moreover, vasculitis markers, platelet activation markers and thrombin generation were normal. Furthermore, almost all symptoms resolved, and none had recurrence of symptoms after further vaccination with mRNA vaccines against Covid-19.

CONCLUSIONS

The combination of headaches and subcutaneous hemorrhage did not represent VITT and no other specific coagulation disorder or intracranial pathology was found. However, symptoms initially mimicking VITT demand vigilance and low threshold for a clinical evaluation combined with platelet counts and D-dimer.

Assessment of immunological anti-platelet factor 4 antibodies for vaccine-induced thrombotic thrombocytopenia (VITT) in a large Australian cohort: A multicenter study comprising 1284 patients

BACKGROUND

Vaccine-induced thrombotic thrombocytopenia (VITT) is a rare complication of adenovirus-based vaccines aimed to prevent and minimize COVID-19 and related pathophysiology.

OBJECTIVES

To describe patterns of testing for anti-platelet factor 4 (PF4) antibodies using various ELISA assays in a large Australian cohort and comparative functional platelet activation assays in a subset.

PATIENTS/METHODS

Asserachrom HPIA IgG ELISA was performed in 1284 patients over a period of 12 months, supplemented in select cohorts by comparative ELISA using three other methods (n = 78-179), three different functional assays (flow cytometry, serotonin release assay, and/or Multiplate; n = 476), and rapid immunological chemiluminescence anti-PF4 assay (n = 460), in a multicenter study.

RESULTS

For first episode presentations, 190/1284 (14.8%) ELISA tests were positive. Conversely, most (445/460; 96.7%) chemiluminescence anti-PF4 test results were negative. All functional assays showed associations of higher median ELISA optical density with functional positivity and with high rates of ELISA positivity (64.0% to 85.2%). Data also identified functional positivity in 14.8%-36.0% of ELISA negative samples, suggesting false negative VITT by HPIA IgG ELISA in upward of one third of assessable cases.

CONCLUSION

To our knowledge, this is the largest multicenter evaluation of anti-PF4 testing for investigation of VITT. Discrepancies in test results (ELISA vs. ELISA or ELISA vs. functional assay) in some patients highlighted limitations in relying on single methods (ELISA and functional) for PF4 antibody detection in VITT, and also highlights the variability in phenotypic test presentation and pathomechanism of VITT.

Severe Thrombocytopenia, Thrombosis and Anti-PF4 Antibody after Pfizer-BioNTech COVID-19 mRNA Vaccine Booster-Is It Vaccine-Induced Immune Thrombotic Thrombocytopenia?

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a serious and life-threatening complication occurring after adenovirus-vector COVID-19 vaccines, and is rarely reported after other vaccine types. Herein, we report a case of possible VITT after the Pfizer-BioNTech mRNA vaccine booster, who presented with extensive lower limb deep vein thrombosis, severe thrombocytopenia, markedly elevated D-dimer and positive anti-PF4 antibody occurring 2 weeks post-vaccination, concurrent with a lupus anticoagulant. A complete recovery was made after intravenous immunoglobulin, prednisolone and anticoagulation with the oral direct Xa inhibitor rivaroxaban. The presenting features of VITT may overlap with those of antiphospholipid syndrome associated with anti-PF4 and immune thrombocytopenia. We discuss the diagnostic considerations in VITT and highlight the challenges of performing VITT confirmatory assays in non-specialized settings. The set of five diagnostic criteria for VITT is a useful tool for guiding initial management, but may potentially include patients without VITT. The bleeding risks of severe thrombocytopenia in the face of thrombosis, requiring anticoagulant therapy, present a clinical challenge, but early recognition and management can potentially lead to favorable outcomes.

Potential mechanisms of vaccine-induced thrombosis

Vaccine-induced immune thrombocytopenia and thrombosis (VITT) is a rare syndrome characterized by high-titer anti-platelet factor 4 (PF4) antibodies, thrombocytopenia and arterial and venous thrombosis in unusual sites, as cerebral venous sinuses and splanchnic veins. VITT has been described to occur almost exclusively after administration of ChAdOx1 nCoV-19 and Ad26.COV2.S adenovirus vector- based COVID-19 vaccines. Clinical and laboratory features of VITT resemble those of heparin-induced thrombocytopenia (HIT). It has been hypothesized that negatively charged polyadenylated hexone proteins of the AdV vectors could act as heparin to induce the conformational changes of PF4 molecule that lead to the formation of anti-PF4/polyanion antibodies. The anti-PF4 immune response in VITT is fostered by the presence of a proinflammatory milieu, elicited by some impurities found in ChAdOx1 nCoV-19 vaccine, as well as by soluble spike protein resulting from alternative splice events. Anti-PF4 antibodies bind PF4, forming immune complexes which activate platelets, monocytes and granulocytes, resulting in the VITT's immunothrombosis. The reason why only a tiny minority of patents receiving AdV-based COVID-19 vaccines develop VITT is still unknown. It has been hypothesized that individual intrinsic factors, either acquired (i.e., pre-priming of B cells to produce anti-PF4 antibodies by previous contacts with bacteria or viruses) or inherited (i.e., differences in platelet T-cell ubiquitin ligand-2 [TULA-2] expression) can predispose a few subjects to develop VITT. A better knowledge of the mechanistic basis of VITT is essential to improve the safety and the effectiveness of future vaccines and gene therapies using adenovirus vectors.

Factors related to the serious adverse events in patients visiting the emergency department after ChAdOx1 and mRNA COVID-19 vaccination

Introduction

We investigated the clinical characteristics, outcomes and factors related to the serious adverse events (AEs) of patients visiting the emergency department (ED) with various AEs after ChAdOx1 and mRNA COVID-19 vaccination.

Methods

Patients with AEs who visited the ED between March 2021 and September 2021 were selected from three EDs. The clinical data of these patients were collected by retrospectively reviewing medical records. Serious adverse events (AEs) were defined as any adverse medical events that led to hospital admission.

Results

A total of 3572 patients visited the ED with AEs; 69.6% were administered mRNA vaccines, and the median (IQR) age was 48 (31–63) years. Regarding chief complaints, chest pain/discomfort (43.7%) was most common in the mRNA vaccines group, while fever (15.8%) was more commonly presented in the ChAdOx1 group. Most patients (93.9%) were discharged from the ED. In multivariate analysis, age ≥70 years, days from vaccination to ED visit ≥8 days, fever and dyspnea as chief complaints were higher independent risk factors for serious AEs (OR 27.94, OR 2.55, OR 1.95 and OR 2.18: p < 0.001, p < 0.001, p = 0.003 and p = 0.003, respectively).

Conclusion

Most patients who visited the ED with AEs after vaccination were discharged from the ED regardless of the type of vaccine. Emergency physicians need to differentiate serious AEs and consider factors that may require admission to the ED.

Elevated NETs and Calprotectin Levels after ChAdOx1 nCoV-19 Vaccination Correlate with the Severity of Side Effects

ChAdOx1 nCoV-19 vaccination has been associated with the rare side effect; vaccine-induced immune thrombotic thrombocytopenia (VITT). The mechanism of thrombosis in VITT is associated with high levels of neutrophil extracellular traps (NETs). The present study examines whether key markers for NETosis, such as H3-NETs and calprotectin, as well as syndecan-1 for endotheliopathy, can be used as prognostic factors to predict the severity of complications associated with ChAdOx1 vaccination. Five patients with VITT, 10 with prolonged symptoms and cutaneous hemorrhages but without VITT, and 15 with only brief and mild symptoms after the vaccination were examined. Levels of H3-NETs and calprotectin in the vaccinated individuals were markedly increased in VITT patients compared to vaccinees with milder vaccination-associated symptoms, and a strong correlation (r ≥ 0.745, p < 0.001) was found with severity of vaccination side effects. Syndecan-1 levels were also positively correlated (r = 0.590, p < 0.001) in vaccinees to side effects after ChAdOx1 nCoV-19 vaccination. We hypothesize that the inflammatory markers NETs and calprotectin may be used as confirmatory tests in diagnosing VITT.

Brain dural arteriovenous fistulas in the COVID-19 Era: A warning and rationale for association

Objectives

Brain dural arteriovenous fistulas(bDAVFs) are anomalous connections between dural arteries and cerebral veins or sinuses. Cerebral venous thrombosis(CVT) often precedes or coincides with bDAVFs and is considered a risk factor for these vascular malformations. Recently, vaccine-induced thrombotic thrombocytopenia causing CVTs has been associated with COVID-19 vaccines. Concurrently with the start of massive vaccination in our region, we have observed a fivefold increase in the average incidence of bDAVFs. Our objective is to raise awareness of the potential involvement of COVID-19 vaccines in the pathogenesis of bDAVF.

Methods

A retrospective review of demographic, clinical, radiological, COVID-19 infection and vaccination data of patients diagnosed with bDAVFs between 2011 and 2021 was conducted. Patients were divided into two cohorts according to their belonging to pre- or post-COVID-19 vaccination times. Cohorts were compared for bDAVFs incidences and demographic and clinical features.

Results

Twenty-one bDAVFs were diagnosed between 2011 and 2021, 7 of which in 2021. The mean age was 57.7 years, and 62 % were males. All cases except one were treated; of them, 85 % exclusively managed with surgery. All treated cases were successfully occluded. The incidence in 2021 was significantly higher than that in the prevaccination period (1.72 vs 0.35/100,000/year;p = 0.036; 95 %Confidence Interval = 0.09–2.66). Cohorts were not different in age, sex, hemorrhagic presentation, dural sinus thrombosis or presence of prothrombotic or cardiovascular risk factors.

Conclusion

The significant increase in the incidence of bDAVF following general vaccination policies against COVID-19 observed in our region suggests a potential correlation between these two facts. Our findings need confirmation from larger cohorts and further pathogenic research.

Acute ischemic stroke and vaccine-induced immune thrombotic thrombocytopenia post COVID-19 vaccination; a systematic review

Introduction

One of the rare but potentially serious side effects of COVID-19 vaccination is arterial and venous thrombosis. Acute ischemic stroke (AIS) cases have been reported post COVID-19 vaccination. Herein, we systematically reviewed the reported cases of AIS after COVID-19 vaccination.

Method

This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. We searched PubMed and Scopus until April 14, 2022 to find studies that reported AIS post COVID-19 vaccination.

Results

We found 447 articles. From those, 140 duplicates were removed. After screening and excluding irrelevant articles, 29 studies (43 patients) were identified to be included. From all cases, 22 patients (51.1%) were diagnosed with AIS associated with Vaccine-induced immune thrombotic thrombocytopenia (VITT). Among AIS associated with VITT group, all received viral vector vaccines except one. The majority of cases with AIS and VITT were female (17 cases, 77.2%) and aged below 60 years (15 cases, 68%). Fourteen patients (32.5%) had additional thrombosis in other sites. Four of them (0.09%) showed concurrent CVST and ischemic stroke. Hemorrhagic transformation following AIS occurred in 7 patients (16.27%). Among 43 patients with AIS, at least 6 patients (14%) died during hospital admission.

Conclusion

AIS has been reported as a rare complication within 4 weeks post COVID-19 vaccination, particularly with viral vector vaccines. Health care providers should be familiar with this rare consequence of COVID-19 vaccination in particular in the context of VITT to make a timely diagnosis and appropriate treatment plan.

Detection of Platelet-Activating Antibodies Associated with Vaccine-Induced Thrombotic Thrombocytopenia by Flow Cytometry: An Italian Experience

Rare cases of thrombocytopenia and thrombosis after anti-COVID-19 adenovirus-associated mRNA vaccines (VITT) due to platelet-activating anti-platelet-factor 4 (PF4)/polyanion antibodies have been reported. VITT laboratory diagnosis, similarly to heparin-induced thrombocytopenia (HIT) diagnosis, requires immunoassays for anti-PF4/polyanion antibodies identification, such as ELISA assays and platelet-activating functional tests, such as heparin-induced platelet activation test (HIPA), to confirm their pathogenicity. We compared the flow cytometry (FC) measurement of platelet p-selectin exposure to the gold standard functional test HIPA for diagnosis confirmation in 13 patients with a clinical VITT syndrome (6M/7F; median age 56 (33–78)) who resulted positive to anti-PF4/polyanion antibodies ELISA assays (12/13). FC and HIPA similarly identified three different patterns: (1) a typical non-heparin-dependent VITT pattern (seven and six patients by FC and HIPA, respectively); (2) low/no platelet activation in patients under IvIg therapy (five out of five and two out of four patients by FC and HIPA, respectively); (3) a HIT pattern. Antibodies investigated by FC became negative after 7, 17, and 24 days of therapy in three patients. FC measurement of P-selectin exposure was as sensitive as HIPA but simpler to detect anti-PF4/polyanion antibodies in VITT patients. FC could reliably discriminate VITT from HIT, thus helping for the choice of the anticoagulant.

Vaccine‐induced prothrombotic immune thrombocytopenia without thrombosis may not require immune modulatory therapy: A case report

Background

Vaccine‐induced immune thrombotic thrombocytopenia (VITT) is a rare complication of the ChAdOx1 nCoV‐19 and Ad26.COV2.S COVID‐19 vaccines. It presents most commonly with severe thrombocytopenia and thrombotic complications with extremely high D‐dimer levels 5–30 days after vaccination. We report a patient who presented with mild thrombocytopenia and minimally elevated D‐dimer levels without thrombosis, but who tested positive for antiplatelet factor 4 (PF4) platelet‐activating antibodies on a PF4‐enhanced serotonin‐release assay.

Key Clinical Question

Is immunomodulation necessary in patients who present without thrombosis?

Clinical Approach and Conclusions

Treatment with rivaroxaban alone was followed by platelet normalization despite persistence of anti‐PF4 antibodies. This case provides support that vaccination for COVID‐19 can induce a broad, heterogeneous prothrombotic disorder characterized by anti‐PF4 platelet‐activating antibodies that shares features with classical heparin‐induced thrombocytopenia (HIT) and autoimmune HIT syndromes and that immunomodulation may not be required in those without thrombosis.

Anti-severe acute respiratory syndrome coronavirus-2 adenoviral-vector vaccines trigger subclinical antiplatelet autoimmunity and increase of soluble platelet activation markers

To slow down the coronavirus disease 2019 (COVID-19) pandemic an unequalled vaccination campaign was initiated. Despite proven efficacy and safety, a rare but potentially fatal complication of adenoviral-vector vaccines, called vaccine-induced immune thrombotic thrombocytopenia (VITT), has emerged the pathogenesis of which seems to be related to the development of platelet-activating anti-platelet factor 4 (PF4) antibodies. While a few studies have evaluated the incidence of anti-PF4 positivity in anti-severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) vaccine recipients, to date no studies have assessed whether an antiplatelet immunological response develops and if this associates with platelet and blood clotting activation. We carried out a prospective study in healthy subjects who received the first dose of ChAdOx1 or Ad26.COV2.S or BNT162b2 vaccines to evaluate platelet-specific and non-specific immune response and in vivo platelet activation and blood clotting activation. Individuals receiving ChAdOx1 and, less so, Ad26.COV2.S developed with high frequency auto- or alloantiplatelet antibodies, increased circulating platelet-derived microvesicles and soluble P-selectin associated with mild blood clotting activation. Our study shows that an immunological reaction involving platelets is not uncommon in individuals receiving anti-SARS-CoV-2 vaccination, especially after ChAdOx1 and Ad26.COV2.S, and that it associates with in vivo platelet and blood clotting activation.

Safety of Global SARS-CoV-2 Vaccines, a Meta-Analysis

(1) Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines were developed in only a short amount of time and were widely distributed. We conducted this meta-analysis to understand the safety of SARS-CoV-2 vaccines. (2) Methods: We searched the corresponding literature published from 1 January 2020 to 20 October 2021. Information of adverse events (AEs) of each selected work was collected. The quality and bias of studies was evaluated, and meta-analysis was carried out by using Stata 17.0. (3) Results: Totally, 11,451 articles were retrieved, and 53 of them were included for analysis. The incidence rate of AEs was 20.05–94.48%. The incidence rate of vascular events increased after viral vector vaccination, while the incidence rate of vascular events decreased after mRNA vaccination. Viral vector vaccine had a higher AE rate compared to mRNA vaccines and inactivated vaccines. In most circumstances, the incidence of AEs was higher in older people, female and after the second dose. The sensitivity of meta-analysis was acceptable; however, the literature was subject to a certain publication bias. (4) Conclusions: The safety of SARS-CoV-2 vaccines was acceptable. The incidence of allergic symptoms and cardiovascular and cerebrovascular symptoms was low. Viral vector vaccine had a higher risk of leading to thrombosis events. The understanding of SARS-CoV-2 vaccine AEs should be enhanced, so as to promote the vaccination.

Immunogenicity and clinical features relating to BNT162b2 messenger RNA COVID-19 vaccine, Ad26.COV2.S and ChAdOx1 adenoviral vector COVID-19 vaccines: a systematic review of non-interventional studies

Background

Vaccination against Coronavirus disease 2019 (COVID-19) is an important means of controlling the pandemic, however they are expected to stimulate immune responses when administered to confer immunity. In this review, we evaluated the clinical and laboratory features associated with BNT162b2 messenger RNA COVID-19 vaccine, Ad26.COV2.S and ChAdOx1 adenoviral vector COVID-19 vaccines, to determine their immunogenicity. Demographic distribution of pathogenic autoimmune response and time interval between vaccination and onset of symptoms were also assessed. This was to identify; persons at risk of developing auto-immune reactions and  markers to enhanced occurrence of this event.

Main body

Using relevant keywords, search was conducted in the databases of PubMed, Scopus, Web of Science and Google scholar from November 2020 to May 31, 2021. Additional article was also identified through hand-searching of reference lists, and the review was conducted in line with Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines 2009. Study outcome measures were presence of antibodies after vaccination and evidence of autoimmune reactions, therefore studies relating these measures were considered eligible for this review. Studies showed stimulation of immune response with administration of BNT162b2 mRNA vaccine, ChAdOx1 and Ad26.COV2-S adenovirus vector-based vaccines. Aside SARS-CoV-2 spike protein antibodies, elevated D-dimers, presence of PF4 and low fibrinogen were most commonly seen laboratory features in persons with autoimmune reactions following vaccination. In addition, thrombotic thrombocytopenia was the commonest clinical features observed with ChAdOx1 and Ad26.COV2-S adenovirus vector-based vaccines. Findings from this study also suggest higher susceptibility of women of 22-60 years to the pathogenic immunogenicity that may particular result from exposure to ChAdOx1 and Ad26.COV2-S adenovirus vector-based vaccines. Time interval of 4-37 days was mostly observed between vaccination and occurrence of a symptom.

Conclusion

Immune thrombotic thrombocytopenia and other PF4 dependent syndrome are likely associated with ChAdOx1 and Ad26.COV2.S adenovirus vector vaccines, mostly occurring in women usually within 4-37 days of first dose of vaccine. Enhanced knowledge about vaccine adverse effects and its distribution is crucial for effective vaccination strategies.

New presentations and exacerbations of immune thrombocytopenia after coronavirus disease 2019 vaccinations: the Taiwan experience

Immune thrombocytopenia (ITP) is a condition that is distinct from thrombosis with thrombocytopenia syndrome (TTS) that may also occur after coronavirus disease 2019 (COVID-19) vaccinations. Previous reports revealed an increased ITP incidence after ChAdOx1, a vaccine for COVID-19. Our study aimed to highlight the key features of ITP after COVID-19 vaccination. From April to October 2021, we collected data on 23 patients, including nine men and 14 women, with ITP from five hospitals across Taiwan who received either the ChAdOx1 or mRNA-1273 vaccine before development or exacerbation of ITP. Our findings revealed that both ChAdOx1 and mRNA-1273 vaccines were associated with ITP. Many patients responded well to steroids and immune suppressants, which may also suggest that the nature of thrombocytopenia is more like ITP rather than TTS. Lack of thrombosis, low D-dimer level, and negative anti-PF4 result could help to exclude TTS, which is also a rare but a far more lethal condition.

COVID-19, Vaccines, and Thrombotic Events: A Narrative Review

The coronavirus disease 2019 (COVID-19), a deadly pandemic that has affected millions of people worldwide, is associated with cardiovascular complications, including venous and arterial thromboembolic events. Viral spike proteins, in fact, may promote the release of prothrombotic and inflammatory mediators. Vaccines, coding for the spike protein, are the primary means for preventing COVID-19. However, some unexpected thrombotic events at unusual sites, most frequently located in the cerebral venous sinus but also splanchnic, with associated thrombocytopenia, have emerged in subjects who received adenovirus-based vaccines, especially in fertile women. This clinical entity was soon recognized as a new syndrome, named vaccine-induced immune thrombotic thrombocytopenia, probably caused by cross-reacting anti-platelet factor-4 antibodies activating platelets. For this reason, the regulatory agencies of various countries restricted the use of adenovirus-based vaccines to some age groups. The prevailing opinion of most experts, however, is that the risk of developing COVID-19, including thrombotic complications, clearly outweighs this potential risk. This point-of-view aims at providing a narrative review of epidemiological issues, clinical data, and pathogenetic hypotheses of thrombosis linked to both COVID-19 and its vaccines, helping medical practitioners to offer up-to-date and evidence-based counseling to their often-alarmed patients with acute or chronic cardiovascular thrombotic events.

Laboratory testing for platelet factor 4 antibodies: differential utility for diagnosis/exclusion of heparin induced thrombocytopenia versus suspected vaccine induced thrombotic thrombocytopenia

Platelet factor 4 (PF4), a protein stored in the alpha-granules of platelets and released upon activation, forms cationic tetramers that bind with various polymeric anions, including heparin. Some individuals develop antibodies against PF4 in complex with heparin (PF4/H), which potentially lead to the onset of heparin induced thrombocytopenia (HIT). In some patients, this may cause activation and aggregation of platelets, promoting pathological thrombosis, in a process called heparin induced thrombocytopenia with thrombosis ('HITT'). Laboratories can assess for the presence of these antibodies using many PF4 antibody tests, including by enzyme linked immunosorbent assay (ELISA), latex immunoassay (LIA), chemiluminescence immunoassay (CLIA) and even rapid nanoparticle based lateral flow immunoassays. All these assays can identify such antibodies with high sensitivity, but methods may have variable specificity. For example, several studies have shown CLIA assays to have higher specificity to HITT than ELISA assays. Very recently, a new 'HITT-like' syndrome has been described in some individuals receiving adenovirus based COVID-19 (coronavirus disease 2019) vaccines. This condition has been given several names, including vaccine induced thrombotic thrombocytopenia (VITT) and thrombosis with thrombocytopenia syndrome (TTS), and also involves a mechanism mediated by antibodies formed against PF4. These antibodies can also be detected by PF4 antibody tests, but detection sensitivity appears to favour ELISA assays, with most other tests (including CLIA and LIA) not generally capable of detecting such antibodies. Additional functional assays assessing for PF4 mediated platelet activation may also be performed. The current review is focussed on laboratory testing for PF4 antibodies, in particular to distinguishing patterns in HITT versus VITT.

Review and evolution of guidelines for diagnosis of COVID-19 vaccine induced thrombotic thrombocytopenia (VITT)

Coronavirus disease 2019 (COVID-19) is a life-threatening infectious disease caused by Severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2). In response to the still ongoing pandemic outbreak, a number of COVID-19 vaccines have been quickly developed and deployed. Although minor adverse events, either local (e.g., soreness, itch, redness) or systematic (fever, malaise, headache, etc.), are not uncommon following any COVID-19 vaccination, one rare vaccine-associated event can cause fatal consequences due to development of antibodies against platelet factor 4 (PF4), which trigger platelet activation, aggregation, and possible resultant thrombosis, often at unusual vascular sites. Termed thrombosis with thrombocytopenia syndrome (TTS) by reporting government agencies, the term vaccine-induced (immune) thrombotic thrombocytopenia (VITT) is more widely adopted by workers in the field. In response to increasing reports of VITT, several expert groups have formulated guidelines for diagnosis and/or management of VITT. Herein, we review some key guidelines related to diagnosis of VITT, and also provide some commentary on their development and evolution.

Case Report of Cerebral Sinus Thrombosis Related to Immune Thrombotic Thrombocytopenia Following Administration of ChAdOx1 nCoV-19 for Vaccination against COVID-19

Vaccine-induced immune thrombotic thrombocytopenia (VITT) with cerebral venous sinus thrombosis (CVST) has been recently reported after vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We present a case of a patient with fulminant CVST and thrombocytopenia after receiving the ChAdOx1 nCoV-19 vaccine. Although the patient received immediate anticoagulant and intravenous immune globulin treatment, he died within 24 h after hospital admission. VITT and CVST are rare conditions; however, the course may be fatal. Therefore, clinicians should be familiarized with the clinical and laboratory features of VITT.

COVID-19 vaccine-induced immune thrombotic thrombocytopenia: A review

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly transmissible and pathogenic coronavirus responsible for the pandemic coronavirus disease 19 (COVID-19). It has significant impact on human health and public safety along with negative social and economic consequences. Vaccination against SARS-CoV-2 is likely the most effective approach to sustainably control the global COVID-19 pandemic. Vaccination is highly effective in reducing the risk of severe COVID-19 disease. Mass-scale vaccination will help us in attaining herd immunity and will lessen the negative impact of the disease on public health, social and economic conditions. The present pandemic stimulated the development of several effective vaccines based on different platforms. Although the vaccine is safe and efficacious, rare cases of thrombosis and thrombocytopenia following the use of vaccination with the ChAdOx1 CoV-19 vaccine (AstraZeneca, University of Oxford, and Serum Institute of India) or the Ad26.COV2.S vaccine (Janssen/Johnson & Johnson) have been reported globally. This review focussed on the definition, epidemiology, pathogenesis, clinical features, diagnosis, and management of vaccine associated thrombosis.

COVID-19 Vaccination in Children: An Open Question

BACKGROUND

A safe and effective vaccine represents the best way to control the COVID-19 pandemic, which has caused more than 4 million deaths to date. Several vaccines have now been approved worldwide, depending on the country. Being administered to healthy people, anti-SARS-CoV-2 vaccines must meet high safety standards, and this is even more important among the pediatric population in which the risk of developing severe disease is significantly lower than adults. However, vaccination of the pediatric population could help in reducing viral spread in the whole population.

OBJECTIVE

Our narrative review analyzes and discusses the currently available literature on the advantages and disadvantages of COVID-19 vaccination in the pediatric population.

METHODS

A bibliographic research was conducted through Pubmed, Read, and Scopus using COVID-19, SARS-CoV-2, immunization, antibody, COVID-19 vaccine efficacy, COVID-19 vaccine safety, children, adolescents, MIS-C, adverse effects as keywords.

RESULTS

Although children are less susceptible to COVID-19 infection, they can develop serious consequences, including multi-inflammatory syndrome. However, any vaccine-related side effects should be evaluated before administering vaccination to children while ensuring complete safety. To date, adverse effects are reported in adolescents and young adults following vaccination; however, these are mostly isolated reports.

CONCLUSION

Further investigation is needed to establish whether there is indeed a cause-and-effect relationship in the development of vaccine-related adverse effects. However, to date, COVID-19 vaccination is recommended for children and adolescents older than 12 years of age. However, this question is still under debate and involves ethical, political, and social issues.

Cardiovascular and haematological events post COVID-19 vaccination: A systematic review

Since COVID‐19 took a strong hold around the globe causing considerable morbidity and mortality, a lot of effort was dedicated to manufacturing effective vaccines against SARS‐CoV‐2. Many questions have since been raised surrounding the safety of the vaccines, and a lot of media attention to certain side effects. This caused a state of vaccine hesitancy that may prove problematic in the global effort to control the virus. This review was undertaken with the aim of putting together all the reported cardiovascular and haematological events post COVID‐19 vaccination in published literature and to suggest possible mechanisms to explain these rare phenomena.

New-onset autoimmune phenomena post COVID-19 vaccination

Coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to an unprecedented setback for global economy and health. Vaccination is one of the most effective intervention to substantially reduce severe disease and death due to SARS-CoV-2 infection. Vaccination programs are being rolled out globally, but most of these vaccines have been approved without extensive studies on their side effects and efficacy. Recently, new-onset autoimmune phenomena after COVID-19 vaccination have been reported increasingly (e.g., immune thrombotic thrombocytopenia, autoimmune liver diseases, Guillain-Barré syndrome, IgA nephropathy, rheumatoid arthritis and systemic lupus erythematosus, etc.). Molecular mimicry, the production of particular autoantibodies and the role of certain vaccine adjuvants seem to be substantial contributors to autoimmune phenomena. However, whether the association between COVID-19 vaccine and autoimmune manifestations is coincidental or causal remains to be elucidated. Here, we summarize the emerging evidence about autoimmune manifestations occurring in response to certain COVID-19 vaccines. Although information pertaining to the risk of autoimmune disease as a consequence of vaccination is controversial, we merely propose our current understanding of autoimmune manifestations associated with COVID-19 vaccine. In fact, we do not aim to disavow the overwhelming benefits of mass COVID-19 vaccination in preventing COVID-19 morbidity and mortality. These reports could help guide clinical assessment and management of autoimmune manifestations after COVID-19 vaccination.

SARS-CoV-2 vaccine-induced immune thrombotic thrombocytopenia

SARS-CoV-2 vaccines have been carefully developed and significantly alleviate the global pandemic. However, a rare but severe complication after vaccination of adenoviral vector vaccines has attracted worldwide attention. It is characterized by thrombosis at unusual sites (often cerebral or abdominal), thrombocytopenia, and the presence of antibodies against platelet factor 4 (PF4), termed vaccine-induced immune thrombotic thrombocytopenia (VITT). Its pathogenesis is similar to that of heparin-induced thrombocytopenia (HIT). VITT progresses rapidly and has a high mortality rate. Clinicians and the public should raise their vigilance to this disease so that accurate and timely treatment is provided.

Inflammation and Platelet Activation After COVID-19 Vaccines - Possible Mechanisms Behind Vaccine-Induced Immune Thrombocytopenia and Thrombosis

Introduction of vaccines against COVID-19 has provided the most promising chance to control the world-wide COVID-19 pandemic. However, the adenovirus-vector based Oxford/AstraZeneca [ChAdOx1] (AZ) and Johnson & Johnson [Ad26.CoV2.S] COVID-19 vaccines have been linked with serious thromboembolic events combined with thrombocytopenia, denominated Vaccine-induced Immune Thrombocytopenia and Thrombosis (VITT). The pathogenesis of COVID-19 VITT remain incompletely understood; especially the initial events that trigger platelet activation, platelet factor (PF)4 release, complex formation and PF4 antibody production are puzzling. This is a prospective study investigating the impact of different COVID-19 vaccines on inflammation (CRP, TNF-α, IL-1β, IL-6, IL-8, IL-10), vascular endothelial activation (syndecan-1, thrombomodulin, E-selectin, ICAM-1, ICAM-3, VCAM-1), platelet activation (P-selectin, TGF-β, sCD40L) and aggregation (Multiplate^® impedance aggregometry), whole blood coagulation (ROTEM^®), thrombin generation and PF4 antibodies to reveal potential differences between AZ and mRNA vaccines in individuals without VITT. The study included 80 (55 AZ and 55 mRNA) vaccinated individuals and 55 non-vaccinated age- and gender matched healthy controls. The main findings where that both vaccines enhanced inflammation and platelet activation, though AZ vaccination induced a more pronounced increase in several inflammatory and platelet activation markers compared to mRNA vaccination and that post-vaccination thrombin generation was higher following AZ vaccination compared to mRNA vaccination. No difference in neither the PF4 antibody level nor the proportion of individuals with positive PF4 antibodies were observed between the vaccine groups. This is the first study to report enhanced inflammation, platelet activation and thrombin generation following AZ vaccination compared to mRNA vaccination in a head-to-head comparison. We speculate that specific components of the AZ adenovirus vector may serve as initial trigger(s) of (hyper)inflammation, platelet activation and thrombin generation, potentially lowering the threshold for a cascade of events that both trigger complications related to excessive inflammation, platelet and coagulation activation as observed in epidemiological studies and promote development of VITT when combined with high-titer functionally active PF4 antibodies.

Interactions of adenoviruses with platelets and coagulation and the vaccine-induced immune thrombotic thrombocytopenia syndrome

The COVID-19 pandemic has had a heavy impact on global health and economy and vaccination remains the primary way of controlling the infection. During the ongoing vaccination campaign some unexpected thrombotic events have emerged in subjects who had recently received the AstraZeneca (Vaxzevria) vaccine or the Johnson and Johnson (Janssen) vaccine, two adenovirus vector-based vaccines. Epidemiological studies confirm that the observed/expected ratio of these unusual thromboses is abnormally increased, especially in women in fertile age. The characteristics of this complication, with venous thromboses at unusual sites, most frequently in the cerebral vein sinuses but also in splanchnic vessels, often with multiple associated thromboses, thrombocytopenia, and sometimes disseminated intravascular coagulation, are unique and the time course and tumultuous evolution are suggestive of an acute immunological reaction. Indeed, plateletactivating anti-PF4 antibodies have been detected in a large proportion of the affected patients. Several data suggest that adenoviruses may interact with platelets, the endothelium and the blood coagulation system. Here we review interactions between adenoviral vectors and the hemostatic system that are of possible relevance in vaccine-associated thrombotic thrombocytopenia syndrome. We systematically analyze the clinical data on the reported thrombotic complications of adenovirus-based therapeutics and discuss all the current hypotheses on the mechanisms triggering this novel syndrome. Although, considering current evidence, the benefit of vaccination clearly outweighs the potential risks, it is of paramount importance to fully unravel the mechanisms leading to vaccineassociated thrombotic thrombocytopenia syndrome and to identify prognostic factors through further research.

Vaccine-induced thrombosis and thrombocytopenia (VITT) in Ireland: A review of cases and current practices

Since the beginning of the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS CoV-2) virus pandemic, several highly effective and safe vaccines have been produced at remarkable speed. Following global implementation of vaccination programmes, cases of thrombosis with thrombocytopenia following administration of adenoviral vector-based vaccines started being reported. In this review we discuss the known pathogenesis and epidemiology of so-called vaccine induced thrombocytopenia and thrombosis (VITT). We consider the available guidelines, diagnostic laboratory tests and management options for these patients. Finally, we discuss important unanswered questions and areas for future research in this novel pathoclinical entity.

COVID-19 coagulopathies: Human blood proteins mimic SARS-CoV-2 virus, vaccine proteins and bacterial co-infections inducing autoimmunity: Combinations of bacteria and SARS-CoV-2 synergize to induce autoantibodies targeting cardiolipin, cardiolipin-binding proteins, platelet factor 4, prothrombin, and coagulation factors

Severe COVID-19 is often accompanied by coagulopathies such as thrombocytopenia and abnormal clotting. Rarely, such complications follow SARS-CoV-2 vaccination. The cause of these coagulopathies is unknown. It is hypothesized that coagulopathies accompanying SARS-CoV-2 infections and vaccinations result from bacterial co-infections that synergize with virus-induced autoimmunity due to antigenic mimicry of blood proteins by both bacterial and viral antigens. Coagulopathies occur mainly in severe COVID-19 characterized by bacterial co-infections with Streptococci, Staphylococci, Klebsiella, Escherichia coli, and Acinetobacter baumannii. These bacteria express unusually large numbers of antigens mimicking human blood antigens, as do both SARS-CoV-2 and adenoviruses. Bacteria mimic cardiolipin, prothrombin, albumin, and platelet factor 4 (PF4). SARS-CoV-2 mimics complement factors, Rh antigens, platelet phosphodiesterases, Factors IX and X, von Willebrand Factor (VWF), and VWF protease ADAMTS13. Adenoviruses mimic prothrombin and platelet factor 4. Bacterial prophylaxis, avoidance of vaccinating bacterially infected individuals, and antigen deletion for vaccines may reduce coagulopathy risk. Also see the video abstract here: https://youtu.be/zWDOsghrPg8.