@janemc
I’m not convinced by that argument, as Essential thrombocythemia (ET) is not contagious and cannot be transmitted through blood transfusion.

ET is a bone marrow disorder, specifically a type of Myeloproliferative neoplasm. It arises from acquired genetic mutations in a person’s own blood-forming stem cells—most commonly involving genes such as JAK2 mutation, CALR, or MPL.

In particular, the JAK2 V617F mutation is found in the majority of cases of polycythemia vera and in a substantial proportion of patients with ET or myelofibrosis. These mutations develop internally and are not transmitted between individuals.

There is also a growing body of qualitative and clinical research supporting this understanding.
https://my.clevelandclinic.org/health/diseases/24031-essential-thrombocythemia