What hematologic conditions are contraindications for a COVID vaccine?

The short answer is that a history of severe allergic reaction is really the only contraindication to COVID-19 vaccination. Perhaps, patients with systemic mastocytosis might be at increased risk of allergic reaction but I'm not aware of data to support that.

The longer answer is a question of timing...

Agree with the thoughtful answer by Dr. @Dr. First Last. Lack of conclusive data is the main issue for certain specific questions. It is mainly about the timing & which vaccine. Overall, would favor vaccination unless there is a very rare contraindication, across scenarios, along with physical dista...