Anecdotally, most people -- whether they have CF or not -- would be well served to make significant dietary and lifestyle changes. Having a life threatening disease just provides more incentive for this to take precedence over many people's personal mantra of immediate gratification and lack of serious introspection.
This doesn't really have any bearing on the efficacy of vaccines, though. Perhaps certain lifestyle changes do dramatically reduce susceptibility to certain diseases, but that doesn't mean one should also rule out current scientific literature.
I don't rule out current scientific literature. I just keep in mind that it has its own biases and that view informs my interpretation and use of it.
For example, I am not aware of any studies concerning making dietary changes to control inflammation in people with CF. However, I am aware of many drug studies that show that controlling inflammation in people with CF does reduce incidence of infection. Those studies are generally conducted by drug companies, whose agenda is to develop products to sell (in this case, drugs). The detail that reducing inflammation in people with CF also reduces infection is useful information to me. The fact that they only seem to study which drugs can be useful in this regard while apparently completely ignoring diet and lifestyle is something I view as inherent bias in the source.
I am not a drug company with an agenda to develop a product and/or find a good reason to sell high doses of an existing product to very ill people. I am an individual who was once extremely ill and wanted to suffer less. (I had no goal of "getting well" initially. I just wanted to take less medication and be less miserable.) So I parse out which pieces of such studies are useful neutral information and which pieces smack of bias and agenda. "Reduce inflammation to reduce infection" is valuable information. "Take boatloads of our drugs (such high doses they have to run liver tests and closely monitor you)" smacks of agenda and bias and, frankly, callous disregard for my welfare in the pursuit of the almighty dollar.
This doesn't really have any bearing on the efficacy of vaccines, though. Perhaps certain lifestyle changes do dramatically reduce susceptibility to certain diseases, but that doesn't mean one should also rule out current scientific literature.