We aim to identify vaccination invitations that foster trust and improve vaccination uptake overall, especially among ethnic minority groups who are more at risk from coronavirus disease (COVID-19) and less likely to be vaccinated. In a preregistered 4 × 4 mixed-design experiment, we manipulated how much risk-benefit information the message included within-subjects and the message source between-subjects (N = 4,038 U.K. and U.S. participants, 50% ethnic minority). Participants read four vaccine invitations that varied in vaccination risk-benefit information (randomized order): control (no information), benefits only, risk and benefit, and risk and benefit that mentions vulnerable groups. The messages were sent by one of four sources (random allocation): control (health institution), medical professional (unnamed), warm and competent medical professional (unnamed), and named warm and competent medical professional (Sanjay/Lamar). Participants assessed how much they trusted the message and how likely they would be to book their vaccination appointment. Information about vaccination benefits and risks increased trust, especially among ethnic minority groups-for whom the effect replicated within each group. Trust also increased when the message was sent by a warm and competent medical professional relative to a health institution, but the importance of the source mattered less when more information was shared. Our research demonstrates the positive impact of outlining the benefits and disclosing the risks of COVID vaccines in vaccination invitation messages. Having a warm and competent medical professional source can also increase trust, especially where the message is limited in scope. (PsycInfo Database Record (c) 2024 APA, all rights reserved).