Longitudinal Aspects of VITT

Semin Hematol. 2022 Apr;59(2):108-114. doi: 10.1053/j.seminhematol.2022.03.001. Epub 2022 Mar 7.


In hundreds of patients worldwide, vaccination against COVID-19 with adenovirus vector vaccines (ChAdOx1 nCoV-19; Ad26.COV2.S) triggered platelet-activating anti-platelet factor 4 (PF4) antibodies inducing vaccine-induced immune thrombotic thrombocytopenia (VITT). In most VITT patients, platelet-activating anti-PF4-antibodies are transient and the disorder is discrete and non-recurring. However, in some patients platelet-activating antibodies persist, associated with recurrent thrombocytopenia and sometimes with relapse of thrombosis despite therapeutic-dose anticoagulation. Anti-PF4 IgG antibodies measured by enzyme-immunoassay (EIA) are usually detectable for longer than platelet-activating antibodies in functional assays, but duration of detectability is highly assay-dependent. As more than 1 vaccination dose against COVID-19 is required to achieve sufficient protection, at least 69 VITT patients have undergone subsequent vaccination with an mRNA vaccine, with no relevant subsequent increase in anti-PF4 antibody titers, thrombocytopenia, or thrombotic complications. Also, re-exposure to adenoviral vector-based vaccines in 5 VITT patients was not associated with adverse reactions. Although data are limited, vaccination against influenza also appears to be safe. SARS-CoV-2 infection reported in 1 patient with preceding VITT did not influence anti-PF4 antibody levels. We discuss how these temporal characteristics of VITT provide insights into pathogenesis.

Keywords: COVID-19; ChAdOx1 nCoV-19; TTS; VITT; platelet factor 4; vaccination.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ad26COVS1 / adverse effects
  • COVID-19 Vaccines / adverse effects
  • COVID-19* / prevention & control
  • ChAdOx1 nCoV-19 / adverse effects
  • Humans
  • Platelet Factor 4 / adverse effects
  • Purpura, Thrombocytopenic, Idiopathic* / chemically induced
  • SARS-CoV-2
  • Thrombosis* / chemically induced
  • Thrombosis* / complications


  • Ad26COVS1
  • COVID-19 Vaccines
  • Platelet Factor 4
  • ChAdOx1 nCoV-19