BACKGROUND: The US outbreak of coronavirus disease 2019 (COVID-19) accelerated rapidly over a short time to become a public health crisis.
OBJECTIVE: To assess how high-risk adults' COVID-19 knowledge, beliefs, behaviors, and sense of preparedness changed from the onset of the US outbreak (March 13-20, 2020) to the acceleration phase (March 27-April 7, 2020).
DESIGN: Longitudinal, two-wave telephone survey.
PARTICIPANTS: 588 predominately older adults with ≥ 1 chronic condition recruited from 4 active, federally funded studies in Chicago.
MAIN MEASURES: Self-reported knowledge of COVID-19 symptoms and prevention, related beliefs, behaviors, and sense of preparedness.
KEY RESULTS: From the onset to the acceleration phase, participants increasingly perceived COVID-19 to be a serious public health threat, reported more changes to their daily routine and plans, and reported greater preparedness. The proportion of respondents who believed they were "not at all likely" to get the virus decreased slightly (24.9 to 22.4%; p = 0.04), but there was no significant change in the proportion of those who were unable to accurately identify ways to prevent infection (29.2 to 25.7%; p 0.14). In multivariable analyses, black adults and those with lower health literacy were more likely to report less perceived susceptibility to COVID-19 (black adults: relative risk (RR) 1.62, 95% confidence interval (CI) 1.07-2.44, p = 0.02; marginal health literacy: RR 1.96, 95% CI 1.26-3.07, p < 0.01). Individuals with low health literacy remained more likely to feel unprepared for the outbreak (RR 1.80, 95% CI 1.11-2.92, p = 0.02) and to express confidence in the federal government response (RR 2.11, 95% CI 1.49-3.00, p < 0.001) CONCLUSIONS: Adults at higher risk for COVID-19 continue to lack critical knowledge about prevention. While participants reported greater changes to daily routines and plans, disparities continued to exist in perceived susceptibility to COVID-19 and in preparedness. Public health messaging to date may not be effectively reaching vulnerable communities.