Probably it would have a vaccine effect, so the human immune system would then fight the phage which is the opposite of what you want... Using a "live" phage a

Probably it would have a vaccine effect, so the human immune system would then fight the phage which is the opposite of what you want... Using a "live" phage also has the advantage that it would coevolve with the pathogen, the mRNA produced tailocin is always the same and the pathogens would probably become resistant quickly.