Amid calls for pharmaceutical companies to quickly develop a vaccine against the new coronavirus, some researchers are advocating for the use of human challenge trials that would require infecting volunteers with the new virus—even though researchers haven't yet discovered a proven treatment or cure for Covid-19, the disease caused by the new coronavirus.
According to STAT News, the proposal has re-sparked a long-standing debate over whether human challenge trials are ethical in such instances, with some arguing the trials could help to speed vaccine development, and others saying the trails put lives at risk.
Could human challenge trials speed up vaccine development?
Developing a vaccine and securing FDA's approval for the inoculation often is a long process, STAT News reports. In the past, it's taken more than ten years for some vaccines to be developed and receive the required regulatory approvals.
But as the new coronavirus continues to infect people around the world, some researchers are advocating for the use of human challenge trials to accelerate that process.
During the third phase of typical vaccine trials, researchers often test a promising vaccine in tens of thousands of human volunteers, giving half the group the vaccine and the other half a placebo. The volunteers would then go about their normal lives, and researchers would watch to see whether any participants who received the experimental vaccine naturally become infected with the virus. Researchers would follow-up with participants to assess whether infection rates were lower among the vaccinated group when compared with the control group—a process that can take years, USA Today reports.
But in a controlled human infection trial, researchers would administer a potential vaccine to a smaller number of healthy volunteers and intentionally infect those volunteers with the new coronavirus, known as SARS-CoV-2, in a controlled setting. Researchers then would monitor the volunteers to see whether participants' bodies are able to fight off the infection. According to USA Today, such a trial could allow researchers to determine whether a potential vaccine is effective within months.
STAT News reports that researchers first introduced the idea of using controlled human infection trials to test potential vaccines for the new coronavirus in an article published in the Journal of Infectious of Diseases in March. In April, 35 federal lawmakers in a letter sent to HHS and FDA expressed support for such a trial, writing that the agencies should allow controlled human infection trials to help speed research on a new coronavirus vaccine.
Are human challenge trials ethical?
But the idea of conducting human challenge trials has long been controversial, STAT News reports—and such trials are especially provocative when it comes to the new coronavirus. Because human challenge trial participants would be intentionally infected with the SARS-CoV-2—and because there are not yet any proven treatments or cures for Covid-19—some volunteers could develop the disease and potentially die.
Myron Levine—associate dean for global health, vaccinology, and infectious diseases at the University of Maryland—argued that a treatment for Covid-19 would have to be available "before one would undertake a" human challenge trial. Levine, who has conducted human challenge trials for cholera, malaria, and other diseases, noted that even high-performing potential treatments for Covid-19, like Gilead Sciences' remdesivir, have yet to show they "can reliably halt the progression to severe and fatal disease."
Christine Grady, chief of the department of bioethics at NIH's Clinical Center, added that because so little is currently known about Covid-19, a human challenge trial at this stage would be particularly risky for volunteers. "We don't yet know why some people get sick and others don't or why some people get certain manifestations of … [Covid-19] that others don't get," she said. "There's so much emerging information about this sort of clinical course of infection … that it makes an assessment that it's OK to subject a certain age group to risk a little bit too fast for me."
Others have argued that the fact that so many people who become infected with the new coronavirus exhibit few or no symptoms of Covid-19 could make a human challenge trial even more dangerous, because participants would have to be infected with a high enough amount of the virus to ensure they'd develop detectable illness if the potential vaccine doesn't work.
Anna Durbin, a vaccine researcher at Johns Hopkins University, said, "What are your endpoints going to be? You know, do you want to give people pneumonia? I hope not." Durbin continued, "You want people who … definitely know they're sick," but, with the new coronavirus, "we really don't know what" the balance is "between just feeling crappy and then developing pneumonia."
However, Nir Eyal, a professor of bioethics at Rutgers University and an author of the paper advocating for human challenge trials that was published in March, argued that human challenge trials for a vaccine against the new coronavirus wouldn't be as risky as some people may assume. Eyal said the trials would involve only young and healthy volunteers who are at a low risk of developing a severe case of Covid-19 and dying from the disease.
Further, Eyal argued that the health care industry already relies on healthy participants to take on risks for the greater good. "We rely on healthy volunteers to take on risks as organ donors, drug toxicity trial participants, and, in this crisis, emergency medical service volunteers," he said.
And Stanley Plotkin, a professor emeritus of pediatrics at the University of Pennsylvania and a proponent of human challenge trials for a coronavirus vaccine, said there are ethical questions surrounding human participants in typical vaccine trials, as well. "[W]e're talking about two different methods, both of which have faults," Plotkin said, noting that, even in typical Phase 3 vaccine trials, some participants could die from either receiving or not receiving the vaccine.
But when it comes to launching human challenge trials for a vaccine against the new coronavirus, Plotkin said, "[T]he issue from my point of view is to speed up emergency use of vaccines that are shown to be protective."
Similarly, Kathryn Edwards, scientific director of the Vanderbilt University Vaccine Research Program, said the benefits of human challenge trials for a vaccine against the new coronavirus potentially could outweigh the risks.
"We have to understand that [Covid-19] is a serious disease, the mortality and morbidity and the social consequences that are a result of this infection are enormous," Edwards said. "We have to figure out how to stop it," she added. "This is a balancing act" (Branswell, STAT News, 5/1; Weise, USA Today, 5/5).