The Kill Order

SPOILER ALERT: Read after The Maze Runner, The Scorch Trials and The Death Cure
When sun flares hit the Earth, intense heat, toxic radiation and
flooding followed, wiping out much of the human race. Those who survived
live in basic communities in the mountains, hunting for food.

For Mark and his friends, surviving is difficult, and then an enemy
arrives, infecting people with a highly contagious virus. Thousands
die, and the virus is spreading. Worse, it's mutating, and
people are going crazy. It's up to Mark and his friends to find the
enemy - and a cure - before the Flare infects them all ...