This only includes any characters surviving at the end of the current playthrough. You must complete the final section with the eclipse without taking any damage (e.g. pass all QTEs).
It is possible other failed QTEs could lead to lingering injury so I recommend trying to pass all combat encounters and QTEs for this achievement.
Nick can find a med kit while he searches for Joey in the caves. This means later in the game he will either patch up himself or someone else if they are wounded. This means you can have at least one injury up to the Star Chamber and have it circumvented by the finding of the medkit.
Credit to ThePugHybrid for their
guide.