COVID-19 Vaccines: Antibodies & Thrombotic Thrombocytopenia / EUA Request for Youth 12-15

By Kelly Young

Edited by Susan Sadoughi, MD, and André Sofair, MD, MPH

Platelet-activating antibodies are implicated in the rare thrombotic thrombocytopenia observed in some patients after receiving the AstraZeneca ChAdOx1 nCov-19 vaccine, according to research in the New England Journal of Medicine. Researchers propose that the syndrome, which they call "vaccine-induced immune thrombotic thrombocytopenia (VITT)," is similar to autoimmune heparin-induced thrombocytopenia.

The first team studied 11 patients in Germany and Austria who developed thrombotic events after receiving the AstraZeneca vaccine. Nine were women and had a median age of 36 years. None of the patients had received heparin. Six patients died, one from an intracranial hemorrhage. All had moderate-to-severe thrombocytopenia, nine had cerebral venous thrombosis, three had splanchnic-vein thrombosis, and three had pulmonary embolism.

Researchers tested some of these patients plus others suspected of having post-vaccination prothrombotic thrombocytopenia and found they were positive for platelet-activating antibodies directed against platelet factor 4 (PF4)-heparin. These patients also had platelet activation in the presence of PF4, independent of heparin. The authors speculate that free DNA in the vaccine could potentially trigger these PF4-reactive antibodies.

The authors write: "Clinicians should be aware that in some patients, venous or arterial thrombosis can develop at unusual sites such as the brain or abdomen, which becomes clinically apparent approximately 5 to 20 days after vaccination. If such a reaction is accompanied by thrombocytopenia, it can represent an adverse effect of the preceding Covid-19 vaccination." They say that a widely available PF4-heparin antibody test should be used in suspected cases. They offer several treatment options, including high-dose intravenous immune globulin and anticoagulants used for heparin-induced thrombocytopenia.

A separate research team in Norway chronicled five patients with thromboses and severe thrombocytopenia 7 to 10 days after vaccination. Similarly, all patients had high levels of antibodies to PF4-polyanion complexes.

In other COVID-19 vaccine news, Pfizer and BioNTech have asked the FDA to expand the emergency use authorization for their vaccine to include young people aged 12 to 15.