I'm on Ocrelizumab for MS, which wipes out memory B Cells. EBV lives in these cells. Ironically I'm sitting here at the cancer center now getting my semiannual infusion. Anecdotally this drug has made my day-to-day much easier.
It's been amazing. Wish they had it a long time ago.
First, some of the vaccines are simply dangerous as some are live vaccines. I cannot take some travel vaccines because of this: The risk of me simply catching the disease is too great. Same for their drug.
Second, there is some concern about the effectiveness of the vaccines. For example, the covid vaccine: I wound up with an extra booster because they weren't sure how well I was protected. And this can be the case with other vaccines: You might not get the same sort of protection out of it.
The outcome is generally that it isn't worth it to revaccinate folks. And for myself: It isn't that I'm unprotected completely. My immune system is just... hampered. I think the infusions cause more of an issue, but again, isn't worth the revaccination.
I got COVID vaccine and while I had a symptomatic reaction, the results of my antibody tests were concerning. I had my antibodies checked at LabCorp (forget exactly which protein they checked for) and my antibody count was something like 20, while my wife (as the control) had around 12,000.
Some of the most recent research suggests even though the antibody levels are low, there is a good T Cell response still.
You don't lose any immunity you already had, but any potential future immunity is likely blunted.