Yes, bringing in a new adult chicken or baby chicks into your flock means they will be exposed and carry the virus, but it doesn't mean it's absolutely certain they will ever be symptomatic.
As I pointed out, with good care, your chickens can be as healthy as any flock not carrying a virus in their cells.
You do, however, need to be very mindful that carelessness with bio-security can mean exporting the virus to other flocks. Yours isn't nearly as vicious and tenacious as the one my flock carries. But if you don't remember to take measures with foot wear and visitors, the virus can walk away on the soles of shoes, leaving virus along the way for others, possibly someone with chickens, to pick up on their shoes and walk it back to their flock. I think this is how the virus got to my flock.
As I pointed out, with good care, your chickens can be as healthy as any flock not carrying a virus in their cells.
You do, however, need to be very mindful that carelessness with bio-security can mean exporting the virus to other flocks. Yours isn't nearly as vicious and tenacious as the one my flock carries. But if you don't remember to take measures with foot wear and visitors, the virus can walk away on the soles of shoes, leaving virus along the way for others, possibly someone with chickens, to pick up on their shoes and walk it back to their flock. I think this is how the virus got to my flock.