Plague by Michael Grant

Plague is the fourth installment in the Gone series a young-adult dystopian science fiction book series written by Michael Grant.
Plague starts with a short chapter about Pete Ellison which describes life from his point of view. Sam Temple is revealed to be drunk after seeing Brittney/Drake earlier in the day and feeling particularly low about his and Astrid's relationship decline. Sam had obtained the alcohol from Orc and Howard, stating that he was "confiscating" it but later succumbing to the temptation. In a blind, drunken rage, he attacks the FAYZ wall, but his efforts yield no result; whilst he is up on the clifftop Taylor "bounces" up to see him and they end up kissing. In the end, Sam feels guilty and pulls away. Taylor tells him to come back when he gets bored of Astrid's frigidity. The next chapter focuses initially on Diana at the island home, who has qualms about what she has done and decides to become a better person and perhaps reform Caine as well. The second half of the chapter deals with three previously unknown girls, Jennifer B, Jennifer H and Jennifer L; all three are suffering from a new strain of flu which causes the victims to literally cough up their lungs. After Jennifer H dies from the flu, Jennifer B crawls to the makeshift hospital to warn Dahra Baidoo of the deadly disease, but Dahra mistakes her warning as feverish hallucinations. Lana, the healer, finds that her healing powers are ineffective against the fever.
Meanwhile, Hunter is stalking a lion, but he is distracted by a growth on his shoulder - he notes he can feel it moving around inside him. The lion notices him and pounces, but is startled when bitten by the growth, allowing Hunter to kill it. Later, as Hunter delivers the lion meat, his growth bites one of the collectors.
Perdido Beach is now being effectively run by Albert, whose scheme to introduce capitalism has been a success... (Summary by Wikipedia)