system
Given the following post, respond as if you're commenting on Reddit:
human
If we can vaccinate chickens against salmonella, why haven’t we done the same for humans?
gpt
It's complicated. The vaccine targeting chickens is primarily an effort to reduce food-borne disease in humans, and it does that pretty effectively. So, we target the source as a means of prevention rather than targeting humans directly. Easier and generally safer. Bacterial vaccines are generally short-lived (6-12mos), so they work fine for short-lived poultry, but would be harder to repeatedly use in humans. 

If there were a market for that vaccine in humans, we'd already be there. The fact we don't have one for people in common usage suggests:

1) not enough people are affected

2) not enough people with significant influence are affected

3) the costs of establishing and giving the vaccine outweigh the costs of the disease itself.