The popular gameplay mode Infection is coming back to Halo 5. First appearing in Halo 3, it was announced by 343 Industries during their most recent livestream where they talked about upcoming DLC. It starts off with one player being infected while everyone else is normal, and the goal for the infected player is to kill everyone so that they become infected and join the other team. This will be released with the newest DLC, Ghosts of Meridian, which came out today.
Infection was tweaked in Halo 4, going under the new name Flood. This will be the fifth DLC to come out for free since Halo 5 has launched in October 2015. Infection is the most recent mode to make a return to the series, along with the crazy popular Grifball and the upcoming Firefight Warzone mode. The next two DLC packs will be called Memories of Reach and Hog Wild. There is no official release date for Memories of Reach and Hog Wild.