Ross Marquand believes there's "a lot of viability" to theories Judith Grimes (Cailey Fleming) is the first survivor on The Walking Dead immune to the global virus that turns the dead into flesh-hungry walkers. The long-running theory posits Judith, the daughter of Rick (Andrew Lincoln) and Michonne (Danai Gurira) born from a fling between Lori (Sarah Wayne Callies) and Shane (Jon Bernthal), does not carry the virus as she was born roughly 300 days after the initial zombie outbreak. Addressing fan theories Judith could be immune and will survive through the end of The Walking Dead, Marquand admits such speculation "actually makes a lot of sense."
"There's a lot of theories going around about that, and I think that that has a lot of viability to it," Marquand told Serieously when responding to fan-submitted theories at Comic Con Paris. "Like the walkers weren't interested in her for some reason. I think there's a lot of truth to that. So yes, good call."
A year earlier, Marquand's former co-star Tom Payne, who played Jesus, told Serieously Judith's potential immunity could "definitely" take shape as a future storyline.
"Interesting. That got brought up earlier on, actually. Someone thought that Rick might be immune," Payne said. "And I hadn't even thought about that. But I do think that that could be a future storyline in the show, definitely. And I think, yeah, it makes sense that Judith could be immune. That would be cool. It would be kind of funny if she got bit and didn't die and Carl got bit and did die."
In the comic book source material, where Judith died alongside her birth mother at the prison, creator Robert Kirkman did not address immunity. The origin of the virus was never revealed nor was there ever a cure, but a 20-year-plus time jump in the book's final issue revealed walkers were now the minority in a world mostly restored to normal.
Kirkman addressed the lack of an origin for the virus at San Diego Comic-Con 2017, where he suggested The Walking Dead was unlikely to address the virus or a cure in future storylines:
"When we get questions like these [about a cure], we like to not be as definitive as possible because we don't want to reveal anything. But the answers are 'no' and 'no,'" Kirkman said when asked about an origin and a cure. "One, because it's been done on a lot of other zombie stories. And two, because you know it's kind of a mythology-breaking proposition. You don't want that kind of thing as far as somebody being immune. And we have dabbled in that a little bit in the other show [Fear The Walking Dead]."
He continued, "But as far as actually trying to solve the thing, I've always thought that one of the best things about this show is that it's not about scientists and it's not about people that would take that on as a task – because I feel like that's unrelatable. … To go off and try to solve this would be a boring show, so definitely not."
The Walking Dead Universe has since introduced the shadowy CRM organization, and a Season 5 episode of spinoff Fear revealed the apparently expansive organization is looking to build the world. Whether or not that means an attempt to discover a cure remains to be seen, but such a plot could play out in the Rick Grimes movies.