After much work to complete a cure for the zombie plague, Grand Apothecary Putress has discovered a cure. It will be administered across all realms around 12:00PM PST.

Some other important notes:

• The scourge invasion will continue for a few more days.
  
• The prologue event is not over! More to come!!
• Karazhan boss will be up for approximately another week
• Increased the spawn rate of the Necropoli

Source here.