Dissemination of public health information plays an essential role in communicable disease control and prevention. However, widespread and repeated messaging could become counterproductive if it leads to avoidance and disengagement due to message fatigue. Americans have been inundated with accurate and inaccurate COVID-19 information from myriad sources since the start of the pandemic. Using the health belief model (HBM) as a guiding framework, this study examines COVID-19-related message fatigue among adults in the United States who have gotten at least one dose of a COVID-19 vaccine and the association between message fatigue and COVID-19 booster uptake and intentions. A special survey module of The COVID States Project was fielded between August and September 2022 (n = 16,546). Results showed moderately high levels of message fatigue among vaccinated individuals. Message fatigue was negatively associated with the likelihood of having gotten a COVID-19 booster and intentions to do so among those who had not yet received a booster, above and beyond variance explained by the HBM constructs. These findings underscore the importance of monitoring and mitigating COVID-19-related message fatigue in encouraging the public to stay up to date with COVID-19 vaccination.