I'm not sure how to phrase this question... so here are some thoughts I'm having.

Suppose you find a habitable planet, land there and start colonizing. Would we have to bring our bacteria / viruses with us to survive? Like, the idea that it would not be possible to get the flu again; but is therea trade-off? Would other bacteria eventually mutate sufficently to become infectious, and perhaps, would be even worse.

Our immune system would be tested. Assuming there is bacteria on the habital planet, it's not clear what would happen.

I guess the core of my question is: how homogenous is life?