All of this has been done for a long time. There are numerous such attenuated vaccines that consist of an artificially bred non-virulent version of the illness,

All of this has been done for a long time. There are numerous such attenuated vaccines that consist of an artificially bred non-virulent version of the illness, for example the oral vaccine against Polio. Yes, there is a risk that these attenuated agents cause epidemics by themselves, thus vaccination campaigns employing them require close monitoring. Actually, most remaining cases of Polio originate from such attenuated vaccines, while "wild" Polio is nearing extinction.