We experimentally vary signals and senders to identify which combination will increase vaccine demand among a disadvantaged population in the United States-Black and White men without a college education. Our main finding is that laypeople (nonexpert concordant senders) are most effective at promoting vaccination, particularly among those least willing to become vaccinated. This finding points to a trade-off between the higher qualifications of experts on the one hand and the lower social proximity to low-socioeconomic-status populations on the other hand, which may undermine credibility in settings of low trust.