Kaelyn is trying to reinvent herself this year, to stop being the old, timid, shy Kaelyn. Before making decisions, she asks herself, "what would the new Kaelyn do?" The new Kaelyn would visit a sick friend, and try to strengthen that budding friendship. But that friend has the cough, and the unbearable itching. That friend has the virus. That virus is infecting more and more people across the small Canadian island, and soon the World Health Organization is called in to quarantine then. Supply boats get mobbed; riots break out on the docks. People keep getting sick, and the doctors, the immunologists, the WHO, nobody has any idea what's causing it or how to cure it. Almost nobody survives the virus, and with food and medical supplies growing scarce, it's starting to look like nobody will survive not having the virus, either. Kaelyn is trying to hold things together for her family, but her family is falling apart around her. As is everything else. 
 Modern-day setting makes this feel less dystopian or post-apocalyptic, and really it isn't either. It is, in its way, apocalyptic, though: the quarantine isolates the island, making the islanders effectively the only people still around. The unknown virus epidemic is an apocalyptic event, destroying everything and everyone. Things never get super-desperate, but there is looting, and hoarding, and scavenging of food. 
 I wanted to see more from this, though I can't put my finger on what, exactly. The letter-writing format doesn't really work; I think it would have worked better to call it diary format and do away with the gimmick of talking to the old friend. (The old friend reappears at the book's conclusion and the PR copy already calls this the beginning of a new series, so maybe it was just to keep him relevant.) 
 Audience: mostly high-school girls, given the light romance beginning, family dramas, and lack of action. Similar in tone and voice to Life as We Knew It (also similar for scarcity of both goods and people, and epidemic of illnesses); other readalikes include Epitaph Road (fatal illness wiping out full communities), Matched (seemingly-weak female drawing on inner strength), How I Live Now (ditto; also organization in light of disaster). 
 e-ARC via NetGalley.