The Trump administration has launched an "Operation Warp Speed" initiative that ambitiously aims to have 300 million doses of a coronavirus vaccine by January 2021. While pharmaceutical companies around the world are developing 120 different vaccine candidates, only a few thus far have begun testing their vaccines in people. Among those conducting phase one and phase two clinical trials are Moderna Therapeutics, Pfizer, and Inovio Pharmaceuticals in the United States. Phase one and two trials seek to establish the safety of the vaccine and the immune system's reaction to it.

The conventional next step would be phase three trials, in which thousands of participants at risk of the targeted infection are randomized to receive either the vaccine or a control placebo. The trial participants are then monitored by researchers as they go about their usual lives to see how many of the vaccinated people (vs. those in the placebo group) actually come down with the disease. This stately process of evaluation takes a considerable amount of time to unfold.

Human challenge trials, also known as controlled human infection studies, would greatly speed up the process of identifying effective vaccines and treatments for the virus responsible for the COVID-19 pandemic. Consequently, some prominent bioethicists are arguing that it's time to recruit some healthy and willing young people, inject them with various experimental coronavirus vaccines, and then expose them to the virus to see if any of the vaccines work. Instead of waiting around for the virus to find (vaccinated and unvaccinated) folks in the wild—as researchers do in regular phase three trials—human challenge trials speed things up by purposely bringing the virus to the study participants. sci