Wescott, Shelbi. Virulent #1

Lucy King is only an hour away from embarking on the most incredible vacation of her life: white sandy beaches in a tropical paradise, snorkeling and sunbathing in peaceful tranquility. But as Lucy looks forward to her trip, a sinister plot is unfolding that will demolish the world as she knows it. An unknown bioterrorist group unleashes a virus that virtually wipes out the earth's population--leaving Lucy, and a small faction of survivors, trapped inside her high school to wait out the apocalypse