OBJECTIVE Despite the public health value of vaccines, vaccination uptake rates are stagnating. Expected adverse events following immunization are a major source of concern and play a role in the emergence of vaccine hesitancy. Since nocebo mechanisms are involved in the perception of adverse reactions, positive side-effect communication is warranted. The aim of the present study was to compile a comprehensive communication strategy that minimizes expectations of nocebo effects while respecting the informed consent procedure. METHODS In a randomized 2 × 2 between-subject design, 652 participants received information about COVID-19 or influenza vaccination using either standard side-effect messaging or messaging enriched with proven elements of expectation-optimizing framing. A physician presented information online via video. Moderation analyses were conducted to examine effects among particular subpopulations. Expected adverse event ratings following an imagined immunization, cost-benefit ratios of the vaccination, and future vaccination intentions were assessed. RESULTS Information content ratings were equally high in each group. Positive framing significantly decreased adverse event expectations in the COVID-19 information group and raised the cost-benefit ratio in the influenza condition, indicating higher benefits than cost expectations. Moderation analysis revealed that the framed side-effect communication lowered the expected COVID-19 vaccination uptake willingness in individuals with strong anti-vaccination attitudes. CONCLUSIONS Facing the ongoing coronavirus mass vaccinations, positive information frames have a small but significant impact on vaccination concerns while upholding informed consent. Although intervention trials are still pending, this approach could help decrease vaccine hesitancy by reducing fearful expectations. However, it seems that it should not be used without considering vaccination attitudes. (PsycInfo Database Record (c) 2023 APA, all rights reserved).