He just posted photos of his child getting vaccinated, (because Mark Zuckerberg is a responsible, intelligent adult), and the anti-vaxxers responded with their usual paranoid, delusional, incoherent hysteria.
Comments like “I do not believe this at all. Just plain old publicity for vaccines”, “Who is paying him to do this? I’ll bet that baby will get no vaccines”, “I hope you kid dies so you wake up and stop being a CIA puppet”, “Oh that’s good, already has clothes for the baby in the autism colors”, etc.
FYI, vaccines DON’T cause autism, (there is NO scientific evidence for this and overwhelming evidence against), but 2 million children die each year from vaccine-preventable illnesses.