SARS-CoV-2 Human Challenge Trials: Rethinking the Recruitment of Healthy Young Adults First

In the midst of the ongoing Covid-19 pandemic, researchers across the globe are still working to develop effective vaccines. To expedite this process even further, human challenge trials have been proposed by the World Health Organization (WHO) as an alternative to conventional approaches. In such trials, healthy volunteers are deliberately infected with the pathogen of interest, enabling scientists to study the infection process and facilitate further research on treatments or prophylactics, including vaccines. While human challenge trials would offer a collective benefit to society, minimizing the risks is always difficult. Ethical controversy thus inevitably surrounds these trials. Typically, healthy young adults are recruited to serve as the first candidate subjects for human challenge trials because they are generally considered to represent a low-risk population. Here, we present three reasons for doubt about this healthy-young-adults-first criterion and give justification for also recruiting healthy older adults (or not-young adults), meaning those over 30 years of age, to participate in such trials for SARS-CoV-2.