Why social media hasn’t been able to shut down vaccine misinformation

False claims about the dangers of coronavirus vaccines were running rampant on social media even before Americans began receiving their first shots last week — and now the months-long rollout to the entire population is giving bad information even more room to fester.

It started with baseless rumors that the inoculations would kill or sterilize the recipients, alter people’s DNA or fail to keep up with virus mutations. Now it is expanding to more elaborate conspiracy theories in an era already rife with mistrust of government and other institutions. Social...