Normally when a person is diagnosed with a primary immunodeficiency, they do what's known as a Pneumovax Challenge.  They're given a pneumovax pneumonia vaccination, then a month (or whatever interval) later, they're tested to see if they've developed any pneumonia antibody titers.  In my case, since I'd had pneumonia four times that year already, they decided that starting antibody replacement therapy was more important. It is not known with certainty whether I develop antibodies with the vaccinations that I get, but with one exception I haven't had the flu in the last decade.  So I get vaccinated and we hope for the best. The only way we could do a Pneumovax Challenge would be for me to stop the replacement therapy for six months and let my body reset, then do the challenge.  But I'd be extremely vulnerable to infection and would have to isolate.  We're not really interested in doing that.