We recently reported on a 25-year-old female without a history of heparin exposure, presenting with thrombocytopenia, thrombosis, and elevated D-dimer levels 10 days after nine-valent human papillomavirus (HPV) vaccination (Gardasil, Merck and Co). 1 The patient's samples activated platelet factor 4 (PF4)-treated platelets and recognized PF4-polyanion complexes in heparin-induced thrombocytopenia (HIT) ELISA (PF4-polyanion enzyme-linked immunosorbent assay).As previously noted, 1 thrombosis sites included the right internal iliac vein and bilateral pulmonary emboli. When it was recognized that the AUTHOR CONTRIBUTIONS Adam Kanack performed the research studies. Adam Kanack, Ingvild