I have a cool idea but however it is very Lore changing and I would like to tell,

Russia Isn't on very good terms with America or wherever the Zombie Apocalypse is happening and Sent a Squad of undercover soldiers to release a virus which has the potential to kill everyone, and Cure itself once the person is dead, 

allowing Russia to easily take over America or wherever without Resistance

but however the virus backfired, and turned everyone into Zambies, and the squad of soldiers all died except for one lone survivor