Quantifying the effect of Wakefield et al. (1998) on skepticism about MMR vaccine safety in the U.S.

Background: Efforts to trace the rise of childhood vaccine safety concerns in the US often suggest Andrew Wakefield and colleagues' retracted 1998 Lancet study (AW98)-which alleged that the MMR vaccine can cause children to develop autism-as a primary cause of US vaccine skepticism. However, a lack of public opinion data on MMR safety collected before/after AW98's publication obscures whether anecdotal accounts are indicative of a potentially-causal effect.

Methods: We address this problem using a regression discontinuity framework to study change in monthly MMR injury claims (N = 74,850; from 1990-2019) from the Vaccine Adverse Events Reporting System (VAERS) to proxy concern about vaccine safety. Additionally, we suggest a potential mechanism for the effect of AW98 on vaccine skepticism, via automated sentiment analyses of MMR-related news stories (N = 674; from 1996-2000) in major television and newspaper outlets.

Results: AW98 led to an immediate increase of about 70 MMR injury claims cases per month, averaging across six estimation strategies (meta-analytic effect = 70.44 [52.19, 88.75], p < 0.01). Preliminary evidence suggests that the volume of negative media attention to MMR increased in the weeks following AW98's publication, across four estimation strategies (meta-analytic effect = 9.59% [3.66, 15.51], p < 0.01).

Conclusions: Vaccine skepticism increased following the publication of AW98, which was potentially made possible by increased negative media coverage of MMR.

Significance: Childhood vaccine skepticism presents an important challenge to widespread vaccine uptake, and undermines support for pro-vaccine health policies. In addition to advancing our understanding of the previously-obscured origins of US vaccine skepticism, our work cautions that high-profile media attention to inaccurate scientific studies can undermine public confidence in vaccines. We conclude by offering several recommendations that researchers and health communicators might consider to detect and address future threats to vaccine confidence.