Throughout the show's six-season run, "The Walking Dead" has not covered one vital point of the plot, which is how the zombie plague spread in the first place.
Now, most zombie apocalypse theories start out with a patient zero getting infected with a plague that quickly overruns the world, leaving a trail of death and destruction behind it.
However, according to Cinemablend, Cliff Curtis (who appears in the spinoff show "Fear the Walking Dead") has his own theory on how the zombies came to be.
Curtis' theory states that because of government laws requiring children to become immunized, generations of people now have become more and more afraid of sickness and disease that they would want a shot or medication for the slightest problems.
Given this, people believed there was a cure for almost any sickness. Thus, people's immune systems malfunctioned and did not allow the body itself to die, putting the person in a sort of zombie state.
It is certainly a good theory as to how the zombie plague started, but it is known that the writers and producers of both the comic and TV show have gone out of their way not to go into why the walkers are there in the first place.
This pretty much means that fans of the show and comics may never know why this has happened. Which could be a good thing, as this kind of knowledge could ruin the fundamentals of the no-way-out situation the heroes constantly find themselves in.
However, Uproxx reports that "Fear the Walking Dead" has given some insights into the virus' origins. One such insight is that one of the characters on the show, Gloria, has already been turned into a walker.
It wasn't revealed on the show though how exactly she became one. Many rumors have been circulating that Gloria might actually be patient zero for the Los Angeles area. It is believed that Gloria is not patient zero for the entire country, as Tobias reported that other victims have similar symptoms as Gloria.
What makes finding patient zero so important? If scientists are able to get hold of patient zero, its body and blood could be used as a possible vaccine for the virus.
However, with a lot of potential for both shows, it is highly unlikely that much more information about the virus will be revealed any time soon.