Abstract: What harms has COVID-19 misinformation circulating on social media inflicted on the general public’s cognition and attitudes? We investigated this concern by linking exposure to popular COVID-19 misinformation with three adverse cognitive and attitudinal outcomes in four culturally similar Asian societies (i.e., mainland China, Hong Kong, Singapore, and Taiwan) that differ in digital information accessibility. Data collected from an online survey of 4,094 adult respondents in August 2021 demonstrate that exposure to misinformation on popular social media platforms negatively affected respondents’ misbeliefs of and incorrect knowledge of COVID-19 and antivaccine attitudes. Moreover, sharing misinformation was found to mediate the relationship of misinformation exposure and cognition and attitudes. When situating these relationships in the four societies, we found that exposure and sharing were less frequent in societies with free access to digital information but more frequent in societies with restricted accessibility. Implications of these findings for containing the infodemic are discussed.