Retroviruses have particularly high mutation rates, even in virus terms. So this thing will likely evolve and quickly under whatever pressure we put on it.
I was reading a bit of academic stuff about viral vaccines and now I'm thinking we'll have to get all neo-Victorian on this thing.
Hygiene, distance, testing, testing, quarantine. Colonies for anyone unfortunate enough to be an asymptomatic super-spreader. I don't think this level of discipline and organisation is compatible with many aspects of the present world including the widespread availability of military weapons in many countries and extreme grinding poverty.
And what happens even on this island if we have, say, another round of flash flooding in Cumbria?