Here we are again. The shambling hordes are slowly spreading over most of the world, and gradually starting to starve, while some safe enclaves are distributing a cure. We've seen this song and dance before. It usually takes longer though, odd.
Have you looked into the numbers we're seeing? Why, in some nations all of the undead dropped, well, dead-er, at once.
I'm sure it's fine. After all, this is an infection we're talking about. The dead don't rise from their graves or anything...
I'm sure the cure will behave just as consistently as it always has, too. It's not magic, it's science!
Update: I stand corrected. It appears many of the recently-dead have arisen and there has been a worldwide setback in cure progress. I'm told that the nations most advanced in their research retained the most useful data, but the more advanced they were in their efforts the greater the setback. There are no signs, however, that future research will be negatively affected.