We explore the impact of narratives on beliefs and policy opinions through a survey experiment that exposes US subjects to two media-based explanations of the causes of COVID-19. The Lab Narrative ascribes the pandemic to human error and scientific misconduct in a Chinese lab, and the Nature Narrative describes the natural causes of the virus. First, we find that both narratives influence individual beliefs about COVID-19 origins. More precisely, individual beliefs tend to be swayed in the direction of the version of the facts to which one is more exposed generating a potential source of polarization by exposure. Second, only the Nature Narrative unidirectionally affects policy opinions by increasing people’s preferences toward climate protection and trust in science, therefore representing a channel for one-sided polarization by exposure. Finally, we also explore the existence of heterogeneous effects of our narratives, finding that the Lab Narrative leads to opinion polarization between Republican- and Democratic-leaning states on climate change and foreign trade. This indicates the existence of an additional channel that can lead policy opinions to diverge, which we denote polarization by social context.