To end the COVID-19 pandemic, policymakers have relied on various public health messages to boost vaccine take-up rates amongst people across wide political spectra, backgrounds, and worldviews. However, much less is understood about whether these messages affect different people in the same way. One source of heterogeneity is the belief in a just world (BJW), which is the belief that in general, good things happen to good people, and bad things happen to bad people. This study investigates the effectiveness of two common messages of the COVID-19 pandemic: vaccinate to protect yourself and vaccinate to protect others in your community. We then examine whether BJW moderates the effectiveness of these messages. We hypothesize that just-world believers react negatively to the prosocial pro-vaccine message, as it charges individuals with the responsibility to care for others around them. Using an unvaccinated sample of UK residents before vaccines were made widely available (N=526), we demonstrate that the individual-focused message significantly reduces overall vaccine skepticism, and that this effect is more robust for individuals with a low BJW, whereas the community-focused message does not. Our findings highlight the importance of individual differences in the reception of public health messages to reduce COVID-19 vaccine skepticism.