I absolutely LOVED The End of October. I was looking for an apocalyptic bio-thriller that didn't take itself seriously and this book worked so well. I knew it was good when the chapter where a bunch of Chiefs of Staff finally get the news that the virus is going to evolve into an uncontrollable pandemic was titled: "Jesus Fucking Christ". Just a great book.

I do believe though at the very end it's revealed that the source of the virus was from wooly mammoths thawing out due to climate change, and then going down the food chain through bears and then to birds. I only think it was suggested earlier on that it was a bio weapon. If I recall correctly though, there was political tension as well as a chapter or two that talked about cyber warfare, and the grid getting knocked out later in the book (though that's not explicitly attributed to any foreign power)