This might just be the reason they let you into Abel Township at all. You picked up this box-file while running through the hospital - anything labelled CDC is worth taking. It’s got all the notes inside of anything that had been discovered about the zombie virus before major comms networks finally went dark forever. The research makes it clear there’s no chance for a cure… even a vaccine could take decades of work by teams of dedicated researchers. Which is not a thing we have anymore.
The artefact can be found in Season 1 Mission 1: Jolly Alpha Five Niner