Immunity by Erin Bowman

Survivors of a deadly planetary outbreak take on a new, sinister adversary in the white-knuckle sequel to Contagion, which New York Times bestselling author Amie Kaufman called “gripping, thrilling and terrifying in equal measures.”

They thought their nightmare was over, but Thea, Coen, and Nova’s rescue was only the beginning. After being imprisoned on a ship they thought was their ticket to safety, it’s clear that the threat they left behind isn’t as distant as they’d hoped—and this time the entire galaxy is at risk.

Now that threat is about to be unleashed as an act of political warfare. To prevent an interstellar catastrophe, the survivors must harness the evil they faced on the planet Achlys and learn to wield the only weapon they have left: themselves.