It depends on the type of disease, as well as the strength of the immune system.
Vaccinations work well because they introduce the immune system to various inert pathogens, so the immune system is able to recognise those pathogens, when encountered.
Spanish flu was not an isolated or rare instance of healthy people being infected and killed by a virus. It has and is happening today.
Bechamp's work was ground breaking, and many have built on his work over the last century.
I actually think it is just as important to help people in developing countries, to have clean water, better nutrition, and better housing and education, as well as giving them access to vaccines that will save the lives of many.
Its very easy for those in western countries to quibble about how aid is given, particularly when those western countries are home to the multinational corporations that are causing much of the destruction of the food and environment in developing countries.
Your comments are interesting, in light of a post by a numbered person in a previous thread. I am starting to see a pattern here, with your posts and those of this particular number. Worth investing further I think.