5%

It is the year 2093. 5 years ago, there was an explosion in Russia; an unstable chemical was being produced that was supposed to be able to replace fuel in vehicles. After a malfunction in a generator, the chemical went nuclear, wiping Russia from the face of the planet and spreading a highly poisonous gas across all of Asia.
Within days, the poison had spread to Africa, Europe, United States of America, Canada, South America and Australia. Some ninety-five percent of the world's population was infected. Twenty percent died on contact. The rest, brain dead but moving and highly contagious. The final five percent, well, we're just trying to stay alive.