This study aimed to explore whether and how information about COVID-19 vaccines on social media shapes older adults’ perceptions of and attitudes toward vaccinations. The analysis was conducted through the theoretical lens of the social amplification of risk and affect heuristics. A cross-sectional survey of 429 older adults based on a multistage cluster sampling method was conducted in China. Structural equation modeling was applied to examine the effects of information exposure and negative affect on older adults’ risk perceptions and attitudes toward COVID-19 vaccines. In contrast to the hypotheses, the findings indicated that information exposure had a significant negative effect on risk perceptions of vaccine efficacy. Furthermore, negative affect led to a significantly positive increase in older adults’ risk perceptions of vaccine efficacy and vaccine safety. Attitudes toward vaccination were associated with information exposure and risk perceptions of the efficacy of vaccines. The interaction effect suggested that information exposure moderated the effects of negative affect on the risk perception of vaccine efficacy. This study advances previous research on social media exposure and vaccine-related risk perceptions in the societal context of Mainland China. Based on the findings of this study, government agencies and media managers should apply appropriate strategies to promote COVID-19 vaccination among older Chinese adults.