Fifteen years back, a disaster destroyed the next universe over (it's well established in this story that there are multiple worlds with mostly human populations) and led to a huge influx of refugees. These refugees are from a nomadic herder society. They are settled in refugee camps on the edges of most major cities.
Over time the continuing aftereffects of the disaster make the roads between cities effectively impassable and the central government gives way to various local authorities.
1.I'm assuming that each population would be vulnerable to the other's endemic diseases. Which population would be most at risk of suffering dangerous epidemics? (I'm basing the next few questions on my assumption that the refugees are in more trouble than the natives, so please stop me if I'm wrong).
2.If the refugees are more at risk, would there be an easy way for the government to tackle this issue by increasing their resistance? Are food supplements a plausible idea? Given the practical constraints I've outlined above, I can't see mass inoculation by injections as being easy.
3.If a native city suffered a mild flu epidemic, would the camp on the outskirts be screwed? How much danger would someone from another refugee camp be in when they entered the area? If food supplements are plausible, how much effect would it have if he'd stopped taking them a few weeks ago?
I've tried to research this, but everything I've found has focussed on the diseases brought by European settlers to the Americas. The situation isn't similar enough for me to draw confident conclusions.
Thanks in advance for any help you can offer :)