The emergence of viral diseases such as Ebola virus disease, Zika virus disease, and the coronavirus disease (COVID-19) has posed considerable challenges to health care systems around the world. Public health strategy to address emerging infectious diseases has depended in part on human behavior change and yet the perceptions and knowledge motivating that behavior have been at times inconsistent with the latest consensus of peer-reviewed science. Part of that disjuncture likely involves the existence and persistence of past ideas about other diseases. To forecast and prepare for future epidemic and pandemic response, we need to better understand how people approach emerging infectious diseases as objects of public opinion during the periods when such diseases first become salient at a population level. In this essay, we explore two examples of how existing mental models of past infectious diseases appear to have conditioned and constrained public response to novel viral diseases. We review previously reported experiences related to Zika virus in Central America and discuss public opinion data collected in the early months of the COVID-19 pandemic. In the case of Zika virus disease, we assess how thinking about earlier mosquito-borne disease seems to have affected public consideration of the virus in Guatemala. In the case of COVID-19, we assess how previous vaccination behavior for a different disease is associated with intention to obtain vaccination for COVID-19 in the future.