Elijah Woods portrays Clint, a would-be-author who has moved back to his hometown (and mother's house) to be a substitute teacher at the local elementary school. It's bad timing. There has been a contamination at the local factory farm chicken facility and the chicken meant is spreading a zombie-like contagion. The first to get it is a little blonde girl-then all the other grade schoolers are infected. Among the teachers is a possible love interest for Clint, Wade (Rainn Wilson), who is the current boyfriend of that woman, and some other quirky characters. They become trapped in the school while the students try to devour them-and then learn that the entire surrounding area is infected. So even if they do escape there's no safety from the minuscule zombie hordes.
This is more of a tongue-in-cheek horror movie, along the lines of SLITHER. It is very entertaining. COOTIES is, undeniably, the best zombie movie of 2015.