OBJECTIVE: Social norms predict flu vaccination uptake. Social norms are also a shared reality phenomenon that may have epistemic underpinnings, although this possibility has not yet been tested. We examined whether the relationship between perceived social circle vaccine coverage and own vaccination behavior depends on one's need for closure (NFC), or discomfort with uncertainty. METHOD: We recruited a national sample of 300 participants to complete a pair of brief online surveys, the first of which was administered in September 2021 (Wave 1) and the second of which was administered in November 2021 (Wave 2). Participants estimated their social circle's vaccination behavior for the 2020-2021 flu season and reported their own vaccination behavior for the 2021-2022 flu season. Participants also completed a measure of dispositional NFC, along with other measures. RESULTS: Social circle vaccine coverage reported at Wave 1 predicted participants' vaccination behavior reported at Wave 2, and this relationship was moderated by the NFC. As hypothesized, participants with a high NFC were more likely to adhere to their social circles' vaccination norms, as compared to participants with a moderate or low NFC. Additional analyses were conducted to explore other relevant associations. CONCLUSION: Our findings suggest that people's perception of their social circle's vaccination history interacts with their own desire for certainty in the process they use to make vaccination decisions. This raises the possibility that interventions should promote positive social norms and induce epistemic motivations in tandem to promote vaccine uptake. (PsycInfo Database Record (c) 2025 APA, all rights reserved).