An anti-vaxxer who became a poster child for the movement is now urging parents to vaccinate their kids and stop believing the anti-scientific lies. She’s even explaining what caused her own change of heart.

This whole saga began in 2019. When Halloween parties were still possible, Autumn Dayss dressed up as something truly frightening: an anti-vaxxer. Carrying a tiny skeleton, she said she was attending a costume party as “Karen and her non-vaccinated child.” Clever. (And also controversial for some people who thought she was making light of dead babies.)

The costume really didn’t sit well with Texas mother Heather Simpson, who opposed vaccinations. She shot back on Facebook by posting her own costume, which she claimed was the “least scary thing” imaginable: the measles.

That post went viral (ha) as you’d expect — and as she had hoped. Simpson was a hero to the anti-vax crowd and a target for those who saw her as making light of a disease that killed millions of people each year before a vaccine was developed. The virus was nearly eradicated in the United States, but anti-vaxxers like her, spreading baseless lies, brought measles back. 207,000 people died of the preventable disease in 2019.

But here’s a rather shocking update for you: Today, Simpson posted an update on Facebook explaining that she was no longer an anti-vaxxer.