Both private and public benefits result from vaccination for transmissible diseases, such as seasonal influenza, measles, and COVID-19. To help inform vaccination efforts for such diseases, we ask whether social preferences-concerns for the well-being of other people-influence one's decision regarding vaccination. We measure these social preferences for 549 online subjects: We give each subject $4 to play a public-good game and make contributions to public welfare. To the extent that one gets vaccinated out of concern for the health of others, contribution in this game is analogous to an individual's decision to obtain vaccination. We proxy vaccine demand with individuals' delay to initially vaccinate for COVID-19. We collect COVID-19 vaccination history separately to avoid experimenter-demand effects. We find a strong result: Contribution in the public-good game is associated with greater demand to voluntarily receive a first dose, and thus also to vaccinate earlier. Compared to a subject who contributes nothing, one who contributes the maximum ($4) is 48% more likely to obtain a first dose voluntarily in the four-month period that we study (April through August 2021). People who are more pro-social are indeed more likely to take a voluntary COVID-19 vaccination. We thus recommend further research on the use of pro-social preferences to help motivate individuals to vaccinate for transmissible diseases, such as the flu and HPV.