The world of The Walking Dead is getting bigger and bigger, with the show halfway through The Walking Dead Season 6, and the prequel/spinoff series Fear the Walking Dead starting production on Season 2 last week. In both TV shows, and the Robert Kirkman comics they're based on, fans have never been given an explanation as to why the dead started to rise from the Earth, and it seems they never will. That hasn't stopped some from creating their own theories, including Fear the Walking Dead star Cliff Curtis, who shared his thoughts about how the zombie outbreak began in a new interview with Collider. Here's what he had to say, revealing that he isn't "okay" with not knowing how the zombie outbreak begins.

"I'm not okay with that. I want to know how all of this happen. I'm like, 'Come on, guys! Give me the information!' I've got a theory that I read online and thought, 'That's a good one!' It's not on the show, but what I think is a really strong possibility is that all of the government laws around immunization of children and how it's illegal to not be immunized, so that you have all of these kids who, for generations, are immunized, but then something goes wrong and you have thousands and thousands and thousands of people, all around the world, buying these immunizations for flu shots or to fight bacteria or disease, and we've basically become over-immune and our immune system takes over and refuses to let the body die. That's my theory. That means that it's possible that there are people in the world who have not been immunized, and those are the ones who don't carry the disease. That feeds into my idea about the government not responding. It would be a big problem and you'd have to try to contain the situation."
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The closest we've gotten to any explanation was at the end of The Walking Dead's first season, when Rick (Andrew Lincoln) and his crew made it to the Centers for Disease Control (CDC) in Atlanta. Rick learned from Dr. Edwin Jenner (Noah Emmerich) that the virus is inside everyone, and it's triggered by death, meaning that anyone who dies from a zombie bite or any other manner, will be turned into a zombie. Of course, since we will seemingly never find out, one way or another, what started this epidemic, the actor's theory will likely never be proven true or false.

Season 1 of Fear the Walking Dead left off with Madison (Kim Dickens), Travis (Cliff Curtis) and their extended family taking temporary shelter in Strand's (Colman Domingo) gated estate overlooking the Pacific Ocean. As civil unrest continues to grow and the dead take over Los Angeles, Strand prepares to escape to "Abigail," his large yacht moored offshore. Production is currently under way in Mexico, but no story details have been released yet. When asked if his character Travis Manawa has been "changed" by the events of the first season, Cliff Curtis had this to say.

"You can't go through what they've gone through and not be changed. I think Travis is definitely going to have a shift in his priorities and his ideas about what is correct and right. His value system is being challenged deeply right now. At the same time, I think you'll see him be a lot more resilient than you'd expect and a lot tougher. He's not going to give up his belief in humanity and all that is good that easily. The zombies are going to have to tear that from his heart. He's a tough guy, but he doesn't believe in mindless action. He believes in being thoughtful and considering the consequences of your actions. That's what he teaches, and that's what he lives. So, I think he's just going to get tougher and tougher. I hope, anyway. But just like the audience, I have to wait and see."

AMC hasn't announced an exact premiere date for Season 2 of Fear the Walking Dead, but we know it will debut in the spring of 2016. It's possible this show may debut directly after the back half of The Walking Dead Season 6, which returns on Sunday, February 14, but we'll have to wait and see. What do you think about Cliff Curtis' zombie theory for Fear the Walking Dead?