Youths living in crowded impoverished urban areas face higher risk of infection by SARS-CoV-2. This article presents lessons learned from a preventive intervention project intersected by the COVID-19 crisis that moved from a mix-methods study design to online ethnography. The 'home-officed' research team e-witnessed high-school students' daily lives and collaborated in youths' and community-based organisations' responses in the territories where they study and live. Psychosocial distress increased, also driven by the disastrous governmental response to the health and economic crises. There was growing anxiety about meeting friends and dating, with structural limits for sustaining the recommended social distancing, which added to gender/sexualitybased violence. Simultaneously, we observed students becoming relevant actors through co-producing preventive practices, surpassing risk-group notions and combining SARS-CoV-2 prevention with sexuality, gender, racism and mental-health issues. They managed internet-mediated applications to promote critical thinking and collective actions aimed at health promotion among their peers, from their homes. Freire's concept of 'untested-feasibility' fostered researchers', students' and community leaders' imaginations in the face of this unprecedented crisis, thereby enhancing social responses to the epidemic to become rights-based comprehensive dialogical preventive activities. This ongoing intervention-research stresses how prevention sciences can go beyond reduction of this pandemic to a viral event.