We explore the implications of online social endorsement for the Covid-19 vaccination program in the United Kingdom. Vaccine hesitancy is a long-standing problem, but it has assumed great urgency due to the pandemic. By early 2021, the United Kingdom had the world’s highest Covid-19 mortality per million of population. Our survey of a nationally representative sample of UK adults (N = 5,114) measured socio-demographics, social and political attitudes, media diet for getting news about Covid-19, and intention to use social media and personal messaging apps to encourage or discourage vaccination against Covid-19. Cluster analysis identified six distinct media diet groups: news avoiders, mainstream/official news samplers, super seekers, omnivores, the social media dependent, and the TV dependent. We assessed whether these media diets, together with key attitudes, including Covid-19 vaccine hesitancy, conspiracy mentality, and the news-finds-me attitude (meaning giving less priority to active monitoring of news and relying more on one’s online networks of friends for information), predict the intention to encourage or discourage vaccination. Overall, super-seeker and omnivorous media diets are more likely than other media diets to be associated with the online encouragement of vaccination. Combinations of (a) news avoidance and high levels of the news-finds-me attitude and (b) social media dependence and high levels of conspiracy mentality are most likely to be associated with online discouragement of vaccination. In the direct statistical model, a TV-dependent media diet is more likely to be associated with online discouragement of vaccination, but the moderation model shows that a TV-dependent diet most strongly attenuates the relationship between vaccine hesitancy and discouraging vaccination. Our findings support public health communication based on four main methods. First, direct contact, through the post, workplace, or community structures, and through phone counseling via local health services, could reach the news avoiders. Second, TV public information advertisements should point to authoritative information sources, such as National Health Service (NHS) and other public health websites, which should then feature clear and simple ways for people to share material among their online social networks. Third, informative social media campaigns will provide super seekers with good resources to share, while also encouraging the social media dependent to browse away from social media platforms and visit reliable and authoritative online sources. Fourth, social media companies should expand and intensify their removal of vaccine disinformation and anti-vax accounts, and such efforts should be monitored by well-resourced, independent organizations.