History and specifics
In the 23rd century, cyberneticist Robert Williams established a research facility five kilometers from the planet's largest settlement, where he invented Thirty-Seven and other robots. Britt arrived on the planet and began assisting Williams, but secretly she worked to embed a hybrid cybernetic-human zombie virus into the robots.
In 2273, McCoy was invited to Calibus VII to celebrate the pox cure. He, James T. Kirk, Spock and security guards Barnes, Padilla and Emigh traveled to Calibus VII aboard the Conrad. But during their short trip, Britt released her zombie virus, and by the time the shuttle landed, everyone in the colony had been infected. After locating Britt's records in Williams' facility, McCoy developed an aerosol serum that Spock dispersed into the atmosphere with low-orbital rockets to render the virus dormant, but it wasn't a cure. Kirk quarantined the planet under General Order 7. Because Kirk's security guards had been infected, they were obligated to remain. (TOS - Infestation comics: "Issue 1", "Issue 2")