In this chapter, we draw on examples from São Paulo (Brazil) and Santiago (Chile) to explore how, in the context of the current pandemic of COVID-19, grassroots community mobilisation interacted with public health authorities and the State more broadly. For this, we consider the experiences of social movements trying to meet vulnerable communities’ needs in both countries. In the discussion, we argue that, even in contexts of widespread mistrust and abandonment by authorities, the institutionalised forms of interaction between communities and public health services was critical for shaping the nature of grassroots social action and its collaboration with the State. We also discuss how the interaction between the pandemic and co-occurring sociopolitical processes in both countries is reshaping – again – the meanings of community participation.