The Walking Dead: World Beyond continues the franchise's efforts to pretend The Walking Dead season 1's CDC episode never happened. Retaining an element of mystique over the origin of the zombie apocalypse is a key tenet of the Walking Dead franchise. Robert Kirkman's original comics reveal virtually nothing about the outbreak, the wider world, or the science behind the virus, and AMC's The Walking Dead TV show has largely followed the same principles... with the exception of one glaring omission in season 1. In "TS-19," Rick's group come across Atlanta's CDC - arguably the most useful building to be in during a zombie apocalypse.
Only one survivor remains inside, but Dr. Edwin Jenner is on hand to provide a useful rundown of early research into the zombie virus. According to Jenner, the virus invades the brain like meningitis, sending the synapses and body into a shutdown. The brain stem, however, is restarted while the rest of the organ remains inactive, explaining how the undead move about. Since The Walking Dead season 1, Rick and the gang haven't encountered another scientist with the knowledge and resources of Dr. Jenner, but Walking Dead: World Beyond changes that by entering CRM territory. The Civic Republic Military is bringing together the country's best (surviving) scientific minds and giving them labs full of equipment in order to figure out the zombie virus and how to cure it.
Strangely, however, the CRM's research doesn't quite correlate with Dr. Jenner's. In Walking Dead: World Beyond season 2's "Foothold," Dr. Belshaw of the CRM gives Hope Bennett a brief overview of their post-apocalyptic findings. According to Belshaw, the CRM still hasn't figured out "what inside us makes us turn," or how those who die reanimate, which effectively undoes Dr. Jenner's revelations from The Walking Dead season 1. Some might argue that the CRM simply hasn't hit upon Jenner's discoveries yet, but given the group's extensive resources and endless test subjects, not to mention a decade of time passing, make this unlikely. After all, Jenner's findings were taken from a regular MRI scan.
This isn't the first time The Walking Dead has walked back on season 1's CDC episode. For starters, Rick Grimes and his fellow protagonists never mention to newcomers that they know the science behind why corpses reanimate, acting as ignorant as everyone else in the zombie apocalypse. And when scientific types such as the CRM (and even Eugene) have speculated as to the scientific ramifications of the dead walking, their theories have usually opposed Jenner's brain stem findings. Dr. Belshaw's lab is the closest the Walking Dead has come to another CDC scene since 2010, and rather than picking up the same thread, it's like "TS-19" never happened - that The Walking Dead wants viewers to forget how Jenner already discovered what makes the dead turn into undead.
An explanation can perhaps be found in a 2014 THR interview with Robert Kirkman, in which The Walking Dead's creator described season 1's CDC episode as the one thing he'd change given a chance. Though Kirkman praised the core concept, as well as the Dr. Jenner character, he felt the story "gave away too much information." This might account for why The Walking Dead has deliberately ignored Jenner's findings in subsequent seasons, and why The Walking Dead: World Beyond's CRM are far more vague compared to the CDC. Whereas Jenner discovered a very specific process causing victims to reanimate, the CRM still knows nothing of substance, upholding the mystique of the comic books far better.