No one attached to The Walking Dead ever confirmed what caused the zombie outbreak. It’s understood early in the series that a virus spreads through the world, infecting hosts and mutating their DNA. Eventually, a member of the CDC tells Rick, the virus is airborne. But it isn’t confirmed what caused the virus that leads to the outbreak.
Instead, creator Robert Kirkman remains mum on what he believes caused the outbreak in the comics and the show. In January 2020, according to Den of Geek, he allegedly tweeted at a fan that a “space spore” caused the outbreak. But he deleted the supposed tweet and no other explanation was given.
For most fans of The Walking Dead, though, all that matters is that now, zombies can apparently sleep. And that’s pretty wild.
Watch The Walking Dead on Sundays at 9 p.m. EST on AMC.