Hi, my goodness, your husband has a lot going on right now and you too, as the caregiver. My heart goes out to you as this has to be a dreadfully stressful time. The threat of the Covid virus sure adds another dimension to the situation. There are so many of us on immunosuppressants in the same boat.

It’s understandable that you’re upset over the prospect of his immune system being compromised by the reduction of his B-cells with the Rituxan infusions.
As you learned, Rituximab(Rituxan) inhibits B-Cell production, which, given your husband’s condition, he’d certainly want to do. It’s meant to slow the progression of the blood cancer. Waldenstrom and marginal zone lymphoma are lymphoid side cancers producing too many B cells. That in turn churns out antibody proteins in large excess creating problems throughout the rest of the body. Additionally the over producing B cells can crowd out the other components of the bone marrow~the Myeloid side resulting in ever decreasing red blood cell production, neutrophils and platelets, etc..

In a large nutshell, if the B Cells, which are allowed to replicate unchecked, with time they and the products they produce will eventually crowd out everything in the bone marrow. The marrow will lose the ability to make T cells, neutrophils, macrophages, red blood cells and platelets. From my understanding Rituximab only inhibits B cell production. So the immune cells produced by the myelocytes in the marrow would still be producing neutrophils, macrophages, and the lymphoid side would still be producing T cells so there is a good share of immune system functioning and working to some degree.

It would seem to me the risk for complications of the lymphoma/Waldenstrom greatly outweigh the risk from possibly contracting covid. The Rituximab may be necessary if not essential to the treatment of your husband blood cancer.

Regarding the covid vaccination and flu vaccine; Even being on the immunosuppressants I was encouraged to receive the flu vaccine and the both Pfizer Covid shots by my transplant team. A 3rd vaccination was not recommended at this time. While there’s no way to test the effectiveness, it’s the hope that the vaccines will still form a recognizable immune response. There is more to our immune system than just the B cells.

With the diseases your husband has, while his immune system is compromised by the need to treat the more serious condition, the comforting part is he can take direct action himself to protect his health during this time of vulnerability, not only to the Covid-19 but also other viruses and communicable diseases. Continuing to mask in public areas or with unvaccinated people, frequent hand washing, not touching eyes or face, avoiding crowds, distance when talking, etc., are simple yet effective ways to diminish the possibility of getting ill.
I live this way daily, even without the threat of Covid. It’s became a way of life since my bone marrow transplant 2 years ago and hasn’t impacted my ability to enjoy a normal lifestyle.

After writing this, I realized you’d replied about having the 3rd opinion and waiting on further treatment. Did the latest doctor have any recommendations regarding a booster vaccine?