During the COVID-19 pandemic, what initially appeared to be a nonpartisan public health issue quickly morphed into a highly polarized one. Americans’ opinions split along party lines in just a few months, affecting their attitudes, behaviors, and support for various preventative measures and policies.

Why did responses toward COVID-19 become so politically divided so quickly—or at all? We looked at past scientific controversies to find some answers.

Here’s what we know: three main factors usually drive polarization—political elites influencing opinions, trust in public health institutions, and differences in information sources. So, we analyzed data from the Axios/Ipsos Coronavirus Index, which surveyed around 1,000 people almost every week from March 2020 to September 2021, to see how expectations from each factor held up in explaining partisan reactions to COVID-19.

For COVID-19, the big player was trust in public health institutions. But importantly, we saw that over time, trust became more closely tied to political affiliation: Republicans became less, while Democrats became more, trusting towards public health institutions, and particularly so after the 2020 election.

This trend suggests that both elite polarization and general trust in science across political groups are at play. As those factors become more and more tangled together, they might create a vicious cycle where (political) elite resistance to science-based policies has long-term impacts. Breaking this cycle could be crucial for helping us figure out better ways to communicate science during crises, and to reduce political divides and promote unified, evidence-based responses.