I am not on active chemo, but I have read extensively on this subject, and oncologists are nearly uniform in recommending the COVID-19 vaccines for cancer patients (including those on active chemo). And when I was on active chemo, my team told me to get a flu shot (I did). Efficacy of the COVID vaccines, particularly in cases of substantial immunocompromise from certain blood cancers or certain treatments (not usual for solid tumor/CRC patients), is somewhat of an open question, but safety is nearly universally acknowledged. But I would ask this: If your husband got a flu shot without concern or speculation that his immune system would be “overburdened” by the additional “task” promoted by the vaccine, why start worrying now about the COVID-19 vaccine? Also, keep in mind that natural viral infections such as colds, COVID, and the flu, put a burden on the immune system. In fact, I suspect that a tough battle with COVID might well be more “distracting” to the immune system than a vaccination. Finally, keep in mind that while there is some work for the immune system to do when one gets the shot, the body returns to a “ready” state relatively quickly after vaccination—that’s why the side effects don’t last for weeks or months. And that’s why antibodies are persistent and the anamnestic immune response exists. We’re all immune to measles, for example, though we got our vaccinations years ago, and our body isn’t currently “distracted,” by producing measles antibodies (at least not materially “distracted”). Also, the body produces *billions* of lymphocytes and other immune cells. It’s got good reserves for multi-tasking in most cases. That’s why chemo/radiation (immunosuppressive, but usually mildly or moderately so) work for cancer, but—for example—organ transplantation (with attendant very significant immuncompromise from the drugs necessary for transplantation) has been of limited value. It’s all a balance, and the immune system can generally handle a vaccine. I’ve never seen or heard and oncologist worry about the kind of “re-prioritization” that concerns you (though I understand the common sense concept—they advise that you don’t take a flu shot and COVID shot at the same time, for example—but just think it’s not likely in play here).
Finally, while you start with a reasonable premise that that the immune system is working to keep cancer at bay, it’s just speculation that a vaccine might interfere with that. On the other hand, we know that (1) COVID in cancer patients is high(er) risk, and (2) the vaccine works very well. The balance favors the vaccine in nearly all cases I think.
Hope this helps, or at least gives you some things to look into that might be helpful.
7/19: Rectal cancer: Initially staged as IIIA, T2N1M0
Initially approx 4.25 cm, low/mid rectum, mod. well diff. adenocarcinoma
8/22 -10/14 4 rounds FOLFOX neoadjuvant, 3 w/Oxiplatin (lots of side effects/reduced size est. 70-75%)
Switched to neoadjuvant chemorad in 11/19 (Xeloda and approx. IMRT, 60 Gy, 33 fractions)
Trying to achieve cCR.