"The researchers found there was a tradeoff the more people exposed to the virus, the greater the risk that it could spread. But more exposure also meant that more immunity built up within the bridge community, which acted as a barrier to the wider human population."
Not mentioned: the reason the "bridge community" builds up immunity is because its non-immune members die off.
Even more is the vaccine. If a disease has such a high fatality rate, the people tested will be those already infected. This kind of vaccination takes the gamble that someone’s body will get a boost in it’s own fight of the disease. In other words the vaccine will have to be on hand, and rely on finding infections in order to test it.