Hi David
The short answer to your question on effectiveness based on this scientific article is: somewhat less. Although, patients with CML had the best serological response (COVID-19 antibody response) i.e. 75 % of immunized patients achieved necessary protection. 75 % was for the full CML subgroup, apparently there are some differences in persons receiving imatinib or 2nd gen TKI-s. What those differences actually were, was not clearly explained.
BUT! This study assessed the response to Pfizer/Biontech or AstraZeneca vaccine based on single shot only so the picture might be completely different (most likely better) when the person has received two shots as required. This article does not say that CML patients are left defenseless rather that the response may be a bit impaired after one shot.
Another thing to consider. As a CML patient of course we would like to avoid getting infected at all. But, in regards to vaccination, I truly believe that the goal is to avoid hospitalization and serious consequences. The article does not draw any conclusion whether this impaired serological response is in terms of "avoiding infection" or "avoiding hospitalization". Those two things are very different. Having a mildly symptomatic COVID-19 infection as a vaccinated CML patient is something we should be ready for just in case.
I think the reason for an impaired vaccine response lies in the fact that TKI-s somewhat suppress our lymphoid cell linage as well and antibody production (which derives from the lymphoid cells) is not so effective. But if you have general cytopenias due to early phase treatment, e.g. neutropenia (I am a good example of this), I would of course shield myself from COVID-19 just to be sure.
To sum up:
1. the article only analyzed results after one shot for a two-shot vaccine
2. it would be good to have your antibody level tested. It may give you some insight whether additional shots are needed. A third round of shots is currently on the horizon for most vaccines approved in the EU.
Timo