Chemotherapy is a lot like a wildfire. It takes out everything in its way, including what’s beneficial. So, immune systems drop and lay a person’s entire self bare. It’s why the CDC recommends flu shots for chemotherapy patients every six months, as well as supplemental pneumococcal shots.
But that’s for influenza, which has vaccines ready and waiting for it every winter. COVID-19, of course, has no such thing, at least not yet. And it too is a bit like a wildfire in that it does not discriminate over who or what it touches.