- Mitch's wife Beth dies almost within a day after reaching home.
- Mitch's son dies the very same day when Mitch is on his way home from the hospital where Beth just expired.
- While accompanying his daughter Mitch is never seen wearing a mask, which proves that he himself believed that he was immune.
Back in Minnesota, still in quarantine, Mitch asks Mears if he is immune since he has not shown any symptoms and he also asks why they cannot use his blood to make a vaccine. Mears tells him even though his intentions are noble, plasma vaccines are tricky and time consuming to make and are not guaranteed to work Source
In the rest of the plot, this issue about Mitch not having symptoms even being in close proximity with his wife and son, is not addressed.
Hence my question: Was Mitch really immune? If so, how come he was the only character who was immune when the whole world was falling apart due to this virus outbreak?