While vaccine-critical activism has been widely documented and discussed, comparatively little has been said about the concerted response of pro-vaccine activists defending the majority view. This paper explores two case studies of pro-vaccine activism in Australia and the United States (US). It shows how pro-vaccine views and behaviours can take varying forms due to different aims and methods of engagement – oppositional counteractivities in favour of vaccination in Australia, and issue-based advocacy as part of a political alliance in the US. The focus in Australia comes from a pro-science stance and includes ‘skeptics’ against pseudoscience directly opposing vaccine-critical groups. In the US, the focus takes the form of an issue-specific campaign that has arisen from existing pro-vaccine parent blogs and discussion groups pushing for policy change rather than public confrontation. These case studies exemplify how pro-vaccine activism can take varying forms of either reinforcing the mainstream view or countering digression from it. Drawing on qualitative research, this paper aims to examine the types of practices and strategies employed by activists to voice their support of vaccination, and discusses the means, messages, and motivations of pro-vaccine activism. It ends with an argument for why a study – of public support for in addition to studying public opposition to vaccination – can help to better understand vaccination views and behaviours. These findings have wider implications for the study of counter-activism and the polarisation of civil society groups.