Suppose you are young, healthy, employed in a health care system and that your line of work does not require leaving the low-risk comfort of your home. Now suppose that your employer offers you a vaccine. You know there are others in your community who are at greater risk of contracting and dying from Covid-19 than you. Should you accept the dose?

A Covid-19 vaccine developed by Pfizer and BioNTech has received emergency authorization in the United States and has been authorized in the countries, and a vaccine by Moderna is likely to be authorized soon. In spite of this good news, at least for the first couple of years, Covid-19 vaccines will be a scarce resource. Because low-income countries are likely to lose out in the scramble to get access to them, there have been calls for global solidarity. While equitable allocation of vaccines around the world would be ideal, it is unrealistic as a near-term goal.

Experts in infectious disease and public health warn that the Covid-19 pandemic will be with us until there is an effective vaccine, possibly 12 to 18 months in the future. This situation has given rise to calls for human challenge studies, in which healthy volunteers are injected with an experimental vaccine and then infected with the disease to test the vaccine’s efficacy. Is this ethically justifiable?