My 6 year old's Immunologist is recommending that he recieve the Pneumovax 23 because he has a low?

I'm not sure what effect it will have on his sinus infections but it will help his sinus infections from turning into pneumonias which can have much more severe consequences should he contract pneumonia. Upper respiratory infections can lead to pneumonia easily in children. Pneumonia can be fatal in some kids and weaken the lungs permanently in some kids. So in this case it may be better to boost his immunity with an immunization than risk the full blown illness. Immunizations still use a childs immune system, they just do it in a safer way because the "bug" has been either killed or is altered, like a partially killed bacteria, to not bring on a full blown case of the illness. The immune system detects the killed bacteria and fights it, as it would the illness, but the bacteria will not colonize and make him sick because the bacteria is dead but his immune system will build antibodies against it just the same.

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He may get a low grade fever as his immune system kicks in along with, possibly, some minor aches. I would not hesitate to give it to my child. My son had pneumonia when he was 4 and had to be hospitalized and placed on oxygen and have frequent respiratory treatments. He was so sick and he was bluish grey from the lack of oxygen. It started as cold like symptoms and very rapidly progressed to pneumonia. It is not fun to watch your child go through this. Pneumonia vaccinations are relatively safe. They are given quite frequently. Your childs pediatrician must think it is worth the risk for your child to be protected.