  Health misinformation is believed to have contributed to vaccine hesitancy
during the Covid-19 pandemic, highlighting concerns about the role of social
media in polarization and social stability. While previous research has
identified a link between political partisanship and misinformation sharing
online, the interaction between partisanship and how much misinformation people
see within their social networks has not been well studied. As a result, we do
not know whether partisanship drives exposure to misinformation or people
selectively share misinformation despite being exposed to factual content. We
study Twitter discussions about the Covid-19 pandemic, classifying users
ideologically along political and factual dimensions. We find partisan
asymmetries in both sharing behaviors and exposure, with conservatives more
likely to see and share misinformation and moderate liberals seeing the most
factual content. We identify multi-dimensional echo chambers that expose users
to ideologically congruent content; however, the interaction between political
and factual dimensions creates conditions for the highly polarized users --
hardline conservatives and liberals -- to amplify misinformation. Despite this,
misinformation receives less attention than factual content and political
moderates, who represent the bulk of users in our sample, help filter out
misinformation, reducing the amount of low factuality content in the
information ecosystem. Identifying the extent of polarization and how political
ideology can exacerbate misinformation can potentially help public health
experts and policy makers improve their messaging to promote consensus.
