In patients with a history of HIT, how do you counsel them on the use of the AstraZeneca vaccine given reports of unusual thrombosis and association with PF4/heparin antibodies?

Until we know more, it seems prudent to avoid the AstraZeneca and J&J vaccines, particularly if there is a history of HIT. The Pfizer and Moderna vaccines use a different technology and have not been associated with the thrombosis/thrombocytopenia syndrome.