WandaVision and Avengers: Age of Ultron echoed how and what connection Wanda has with the Mind Stone. Then how come she could be susceptible to the zombie virus?
It is not that clear from What If…? episode 5 how Scarlet Witch gets infected from the zombie virus following her connection with the Mind Stone. While Thanos himself destroyed the Mind Stone in Endgame, it managed to remain important to multiple plotlines in the MCU. This potentially popped up due to its connection that still exists for both Vision and Wanda in WandaVision.
After a zombie virus is brought from the Quantum Realm, only a few bands of survivals have been shown with some of the Marvel Cinematic Universe’s heroes been succumbed to the crowd. In What If…?, when the survivors find Vision, he is portrayed as immune to the virus due to his android body. However, since the virus works in a way that it overloads the limbic system of the human brain, the zombies are kept away by the frequency that emits from the Mind Stone. Vision explains that in detail by using the Infinity Stone and he manages to cure the infected people, which demonstrates his ability to do so with the help of Scott Lang’s head.
The origin of Wanda’s power has anyways been obfuscated by the Marvel Cinematic Universe. Avengers: Age of Ultron claimed that Wanda received her powers after the experiments done on Loki’s scepter that had the Mind Stone. In contrast, WandaVision echoed that Wanda always had her powers but they were nearly dormant unless they were ignited by the Mind Stone. Either way, one thing has been established that Wanda is entangled with the Mind Stone, and her ability to create a replica of Vision still remains within her. This simply means that the part of Mind Stone in her could be immune to the zombie virus that has been introduced in What If…?.
Now that it is clear that Scarlet Witch is susceptible to the zombie virus, Vision’s explanation that how Mind Stone keeps the zombies away is greatly simplified. Even Vision’s immunity must be purely based on the prompt that he is an android that cannot be bitten. While Mind Stone emits a natural frequency, Vision will have to make an effort to set up its perimeter. This might explain why Wanda and her connection with the Mind Stone could not make her immune to the zombie virus.
Well, it is backed up with the fact that if Vision destroys himself by removing the Infinity Stone, zombies could cross the barrier that had existed before. While the Infinity Stone is still there, it could no longer save the survivors from getting infected. More information on how exactly the Mind Stone functions against the virus will be given later in the series as it would be a completely different episode of What If…? where a sequel will be set up in the same timeline.
What If…? releases its new episodes every Wednesday on Disney+.