Quantifying the Impact of Misinformation and Vaccine-Skeptical Content on Facebook

Low uptake of the COVID-19 vaccine in the US has been widely attributed to social media misinformation. To evaluate this claim, we introduce a framework combining lab experiments (total N=18,725), crowdsourcing, and machine learning to estimate the causal effect of 13,206 vaccine-related URLs on the vaccination intentions of US Facebook users (N≈233 million). We estimate the impact of misinformation flagged by fact-checkers was 46X less than that of unflagged content that nonetheless encouraged vaccine skepticism. Although misinformation reduced vaccination intentions significantly more when viewed, flagged content’s exposure on Facebook was limited. In contrast, unflagged stories highlighting rare deaths following vaccination were among Facebook’s most-viewed stories. Our work emphasizes the need to scrutinize factually accurate but potentially misleading content in addition to outright falsehoods.