As another comment said there is some implication that prior exposure to other coronaviruses (which would usually be identified as the common cold) can enable a

As another comment said there is some implication that prior exposure to other coronaviruses (which would usually be identified as the common cold) can enable an effective immune response. If that works I wonder if such exposure is evenly distributed around the world or if it's clustered in certain populations? FWIW here in Australia Melbourne has had a fairly significant outbreak but Sydney hasn't, from what I can tell it's basically dumb luck it didn't happen the other way around.