A mass transformation of humanity had begun. It wouldn't be all at once. There wouldn't panicking in the streets or prejudice agains the changed. In fact, most people would get up, go to work, and go to bed, unaware anything had changed at all.
Only roughly one percent or less of humans would ever be aware that any changes occurred at all.
This wasn't some mutant virus that could be contained, or alien invaders that could be fought.
This was a cascade of reality itself.
One person was changed at first, and then, as they interacted with other people, exchanging words, exchanging ideas, it wouldn't have made a difference if the person was wearing a hazmat suit or not, this wasn't a disease, this was reality itself being rewritten. Not just perception, but truly reality was changed, to where if a person had gone back in time, they'd have found people transformed having been that way always.