Vaccines are a hot topic. Vaccines bring up lots of discussion, lots of false information, and a vitriolic passion rarely seen in matters of science and pseudoscience. My first post on this topic was about what vaccines are and and what they do. My second post addressed some of the false information and controversy (with an added bonus of bringing in my lovely sister’s fabulous point of view as a mom of two!) This post will address a question I was asked about whether or not vaccinations are needed after a stem cell transplant.
A friend of mine asked me a question about her friend with non-Hodgkins who was getting a stem cell transplant. He was wondering if he has to get all new immunizations. Since we have been talking about what immunizations (or vaccines) are and what they do, I thought this would be the perfect place to answer this question. Before I start, please keep in mind that I’m a doctor, but not that kind of doctor. This is NOT a medical opinion. Nothing that I say here should be considered medical advice or used in lieu of talking directly to a doctor.
I won’t give medical advice, but I will explain what is known biologically about why immunizations would be needed after a stem cell transplant. I won’t go into a lot of detail (in part because I’m not an expert immunologist) but also because there are some interesting resources I can refer you to:
Remember the description about how vaccines work. They induce a “memory” in the immune system that recognizes the infectious agent if it is encountered and kills it before it can kill you. The cells that are responsible for the immune response and creating this “memory” are made in the bone marrow and circulate in the blood (it’s a convenient system because your circulating blood gets access to most of your body so it can find and attack infectious agents quickly).
Non-Hodgkin’s lymphoma is a blood cancer where white blood cells (also made in the bone marrow) divide out of control. Chemotherapy, one of the main treatments for this kind of cancer, kills the cancer cells circulating in the blood but also kills cells in the bone marrow, including the stem cells responsible for making new blood and immune cells. With high enough doses of chemotherapy, all of the stem cells in the bone marrow are killed along with the cancer cells. The stem cell transplant replaces the stem cells in the bone marrow which make new blood cells – replacing cancerous cells with healthy blood cells. Researchers have found that the memory from immunizations often decreases after a stem cell transplant. Part of this is because the cells that have the memory may be killed as part of the chemotherapy and the new immune cells haven’t encountered the vaccine before so they won’t have the memory. Part of it may be because during treatment the patient is on immuno-suppressives. Part of the reasons also are still being studied or aren’t very clear.
However, either way, it is suggested that immunizations are needed after the transplant – though not necessarily right after transplant. Again, to reiterate, a doctor will have this information and will be able to provide medical advice. I’m just giving some background as to biologically why immunizations may be needed after a stem cell transplant.