They keep calling the disease "pigeon flu" implying it is in the corona virus family like SARS, covid-19, etc but clearly the physical symptoms and high mortality clearly show it is a hemorrhagic fever like Ebola. On an island it would have been very possible to isolate and contain the infected but that would have not allowed the later extreme plot events.
There are some interesting subplots and intriguing characters however, certain decisions made by major characters strain credulity and one character's particularly heinous action is very unbelievable given the person is not a sociopath. There are other characters who attain measures of personal redemption.
All in all it is an OK apocalyptic story but it is clear that the plot was designed all along to achieve a certain ending for certain characters and set the stage for a second possible series..