Public Significance Statement In a 4-wave longitudinal study conducted in the United States and China, we examined the link between risk perception and preventive behavior in the context of the COVID-19 pandemic. We found that although individuals' risk perception had little effect on engagement in preventive behavior in China, it did motivate preventive behavior in the United States, particularly at the early pandemic stage. These findings suggest that the perception-behavior link can be influenced by culture, policy, and stage of a dynamic health hazard, and that campaigns promoting preventive behavior by increasing risk perception are more likely to succeed if implemented early, when risk perception is still in its formative stage.

Controlling the spread of an infectious disease depends critically on the general public's adoption of preventive measures. Theories of health behavior suggest that risk perceptions motivate preventive behavior. The supporting evidence for this causal link is, however, of questionable validity. The COVID-19 pandemic provides a rare opportunity to examine how risk perceptions, preventive behavior, and the link between them develop in a fast-changing risky environment. In a 4-wave longitudinal study conducted in the United States and China, we found that for Chinese participants, there was little relationship between risk perceptions and preventive behavior. This may be a result of the Chinese government's strict control and containment policies and a collectivistic culture that encourages conforming to norms-both of which limit individuals' nonconformist behavior. For U.S. participants, risk perceptions did motivate preventive behavior in the early stage of the pandemic; however, as time went by and the risk of COVID-19 persisted, preventive behavior also led to perception of higher infection risk, which in turn further motivated preventive behavior. Thus, instead of the presumed unidirectional influence from perception to behavior, our results indicate that the two could mutually reinforce each other. Overall, our findings suggest that risk perceptions-at least in the context of a dynamic health hazard-may only motivate preventive behavior at specific stages and under specific conditions. They also highlight the importance of early interventions in promoting preventive behavior.