When he was eighteen, Abie Rohrig decided that he wanted to donate a kidney to save the life of a stranger who needed it. At twenty, he put his name on a list of volunteers for a human-challenge trial that would test the efficacy of a COVID-19 vaccine. A human-challenge trial for a vaccine would be nearly unprecedented: it would entail giving subjects a candidate vaccine against the virus, and then infecting them deliberately to test its efficacy. The side effects would be largely unknown, and the viral infection could be deadly. But, if successful, this experiment could shave months off of the process of vaccine development and save countless lives. In a conversation with his mother, Elaine Perlman, Rohrig points out that many occupations involve taking on risks to help others. But how much risk is too much? Larissa MacFarquhar, who has written extensively about altruism, talks with Marc Lipsitch, an epidemiologist who co-authored a journal article calling for human-challenge trials, and Angela Rasmussen, a virologist who feels that SARS{: .small}-CoV2 is too unknown for any volunteer to meaningfully give informed consent about its risks.