UNITY, Maine — As the heavily armed Unity College students poured out of a classroom Monday night and into the open, they found that their campus was full of shadows, menace — and zombies.

“My advice? Don’t die,” one young man, wearing fatigues and carrying a Nerf dart gun, called to his female companions as they slipped outside into the night.

The Humans vs. Zombies moderated game of tag going on this week on campus may primarily exist as a fun way to blow off steam in the middle of the semester, but a wildlife biology student has taken it more seriously. Senior Kari Lemelin just won a national math award for an epidemiological research project she did based on the game.

The 21-year-old from Killingworth, Conn., used numbers from last fall’s game to make a mathematical model of the spread of disease. Her project, “Modeling a Zombie Outbreak at Unity College,” earned her the Janet L. Anderson Prize, which is given in recognition of outstanding achievement in mathematical and computational biology.

“I was so excited,” she said Monday night of receiving the accolade recently during MathFest, the national meeting of the Mathematical Association of America. “Everyone else at the conference was a math major. I didn’t think I had a chance.”

But her research proved otherwise. Lemelin, who one day would like to study wild animal populations, said that the zombie infestation can most accurately be compared to rabies, a disease that changes its host’s behavior to make it spread more quickly. She used differential equations to examine the speed at which humans were infected by zombies over the course of the game, and said that while zombies aren’t real, epidemiological consequences certainly are.

“Humans want to stay humans, and zombies want to turn everyone into zombies,” she said. “Some individuals are way better at defending themselves, just like a percentage of people have strong immune systems.”

On Monday night, Lemelin moderated a “mission briefing” for the humans, telling them that their survival depended on getting three boxes of supplies from cars parked somewhere on campus. Altogether, there are 123 participants in the college’s annual showdown, which began at midnight Monday and will last until Friday evening. Players try to remain alive — or untagged by the zombies — but if they are caught, they then must “kill,” or tag human players, so that they won’t starve. The game was begun in 2005 at Goucher College in Baltimore and has seen its popularity spread — infectiously, you could say — to colleges, military bases, neighborhoods and camps around the world, according to humansvszombies.org.

Carrie Diaz Eaton, an associate professor of mathematics at Unity, said that using the game to make a research model shows a student’s ability to look outside the usual language of mathematics to solve a problem. She said that she was proud, but not surprised, that Lemelin was awarded for her work.

“She has the ability and the desire to think about a problem, go back and really work on it,” Diaz Eaton said. “She took this idea and made it come alive. Or undead, whichever you prefer.”

Lemelin is not resting on her zombie laurels, but instead is expanding her research this fall to do a meta-analysis of the modeling project, pulling in data from other places that are playing the game.

“The idea is to get a more accurate model,” she said, adding that she appreciates that her college let her get creative with her math. “Unity is a small, tight-knit community. They encourage individuals to learn in whatever way is easiest for them. I really like math, but a math elective I might be a little leery of. Say zombies, though, and I’m all for it.”

She’s not alone. The other students in the briefing room were obviously enthusiastic about the game. Some wore camouflage face paint while others brainstormed survival strategies with their friends.

“Big kids get a chance to act like little kids,” Kalen Musolff of Bath, a first-year conservation law major who proudly reported that he had shot a zombie earlier that day, said.