North of Armageddon by Clint Pereira

Months after the zombie apocalypse, the a few last holdouts flee to Canada and Alaska where it's cold and isolated. With mosquitoes spreading disease and birds falling dead out of the sky, the exiled travelers begin to lose hope that there is a future at all. Meanwhile, in the now-overpopulated bastion of Juneau, a scientist and a detective try to find out the cause of the affliction and hopefully put an end to it.