"In our view, a more likely, albeit partial, explanation for the observed results is media polarization or a ‘broadcasting effect’. Republican-leaning media outlets appear to have downplayed the dangers of the coronavirus as compared to more Democratic outlets. For instance, in early March, Fox News repeatedly claimed that the coronavirus was less dangerous than influenza and even referred to other media reports as a hoax (although some commentators took it more seriously than others, and the organization took the pandemic more seriously by mid-March 2020). Consistent with this messaging about COVID-19, we found that US counties that consumed more Fox News than Democratic-leaning outlets (MSNBC and CNN) exhibited less physical distancing. These findings also remained significant when controlling for counties’ partisanship in terms of 2016 voting. These results, along with self-report data indicating similar findings and evidence indicating a causal link between Fox News viewership and decreased social distancing, suggest that Republican-leaning media downplaying the virus at the start of the pandemic may have signalled to Republicans that they should not take the virus very seriously, in turn potentially in part causing the observed partisan differences. This possibility underscores the importance of considering communication and mass media when designing public health messaging."