More than 25,000 people have volunteered so far to be infected with the novel coronavirus through 1DaySooner, an online recruitment organization, as an aid in testing vaccine candidates to prevent Covid-19. These volunteers know that Covid-19 can cause suffering and even death yet they are stepping forward, willing to risk their lives, because some researchers and academics contend that such experiments in humans could accelerate vaccine development.
As a physician and a scientist who has cared for patients and who has been involved in the development of vaccines, I feel the urgency to get a vaccine approved for global use. And I have deep admiration for the courageous volunteers who are willing to put themselves in danger.
In this situation, however, their sacrifice cannot be justified. Volunteers need to be protected from both known and unknown risks. The effort to develop a vaccine should not be jeopardized by this well-intentioned but unnecessary experiment.
In the context of an ongoing pandemic, the conventional pace of vaccine development frustrates the public, the government, public health experts, vaccine creators, regulators, and others. It is understandable that many are seeking ways to accelerate the demonstration of safety and efficacy of vaccine candidates. The mumps vaccine, considered the fastest vaccine ever developed, took scientists four years to go from collecting viral samples to securing FDA approval in 1967. A decade or longer is more typical. Everyone is hoping that inventing, testing, obtaining approval and producing a Covid-19 vaccine might be on track to set a new record.
The practice of deliberately infecting people with disease, termed “human challenge trials,” has a long history. It is embedded in the origin of the very first vaccine in 1796, when Edward Jenner, an English physician, purposely infected his gardener’s 8-year-old son with cowpox after observing that people previously infected with cowpox, a relatively mild disease, seemed protected from smallpox, one of the deadliest scourges of the time.
Now, in the midst of the coronavirus pandemic, human challenge studies are being considered again.
In the June 1 issue of the Journal of Infectious Diseases, Nir Eyal, Marc Lipsitch, and Peter G. Smith argue that this approach could accelerate the development and approval of a Covid-19 vaccine by many months. That may sound tempting, but human challenge studies with live virus are unlikely to save time. Moreover, there are ethical and practical reasons for not undertaking human challenge studies with this virus. These authors, like 1DaySooner’s volunteers, are well-intentioned but wrong.
Those in favor of human challenge trials propose enrolling as subjects only healthy young adults, since the Covid-19 mortality rate in this group is low. Just 7% of all Covid-19-related deaths in the U.S. have occurred among those aged 25 to 54 years, compared to 80% in those over age 65. Yet the example of fatal infections in health care workers in the prime of life makes clear that even healthy non-elderly adults may succumb to the novel coronavirus.
Human challenge studies are generally contemplated only when rescue with a lifesaving treatment or intervention is available should a vaccine candidate not protect a volunteer from the disease. But there is no cure or treatment against the SARS-CoV-2 virus that can be deployed with confidence, making viral challenge particularly risky and ethically questionable.
Most people, likely including most of the volunteers, tend to think of vaccines as fully effective: They either work or don’t. This belief generally stems from the success of vaccines for childhood diseases like measles and mumps. But some vaccines, especially those for adults, are much less effective: There are seasons when the flu vaccine is only 70% to 80% effective, or sometimes even less. Imagine, for a moment, that a vaccine candidate undergoing testing turns out to generate immunity in 80% of those who receive it. Then 20% will become infected with Covid-19.
An equally disturbing scenario is what if one of the first volunteers dies, either due to the play of chance, a problem with the vaccine, or the individual’s genetic makeup? This is unlikely to happen but it can, and did, in another setting with consequences that stretched far beyond the single tragic death.
In 1999, Jesse Gelsinger volunteered for one of the first gene therapy trials. The 18-year-old had a rare metabolic genetic disorder, but his condition was managed with medication; he was basically healthy. He volunteered for a safety trial of a virus-based gene-therapy — and died as a result. Missteps in the trial, and the subsequent controversy surrounding his death, set the field of gene therapy back by at least two decades. That hiatus deprived a generation of patients with genetic disorders of treatments.
With vaccines already a target of widespread misinformation campaigns, the death of a single volunteer would likely cause even greater damage. From a public health perspective, it would be especially disastrous if it both slowed the race to develop a coronavirus vaccine and fueled the anti-vaccination movement.
There are other ethical considerations. An important principle in human challenge studies is that subjects must give their informed consent in order to take part. That means they should be provided with all the relevant information about the risk they are considering. But that is impossible for such a new disease.
Covid-19 was initially thought to be mainly a respiratory ailment. We now know that it can damage the kidneys, circulatory system, and the heart. It was initially believed that children could not be sickened by SARS-CoV-2, but it now appears that dozens have developed a severe inflammatory syndrome. And we know nothing about potential long-term complications of Covid-19 because the disease has only been in humans for months. Taken together, this means that no volunteer is able to give true informed consent.
Given these risks, there might still be some justification for a human challenge trial if we knew for certain it would accelerate the development of an effective vaccine. But safer trials can get us to a vaccine in the same amount of time without taking on additional risk for volunteers, especially now that some vaccine candidates already have entered Phase 2 clinical trials and several others are close behind.
In a conventional trial, subjects are injected with either the experimental vaccine or placebo. They are then monitored to see if those who got the vaccine are less likely to contract the disease while going about their daily lives. In a human challenge study, things can theoretically happen more quickly, since volunteers are deliberately infected after getting the trial vaccine or placebo.
But human challenge trials take time, too. For Covid-19, subjects would likely have to receive two doses of vaccine (spaced by weeks), wait for potential immunity to develop, then be infected with the live virus and observed for weeks to months. Since the challenge trial would need to start small and be expanded only with great caution because of the risks involved, it would take months to deliver sufficient data. Safety data, in particular, would be lacking, even though this is one of the biggest issues confronting a new vaccine, because the size of the trial would be too small to garner robust safety data and data about adverse effects of the vaccine would be confounded by the administration of the live virus.
There is no short cut for determining safety.
A large-scale, conventional study could likely be conducted just as quickly. In addition, monitoring and interim analyses of conventional trials raise the possibility of some kind of “conditional” or “emergency use” approval while the trials continue. If that happened, a vaccine might be available for certain high-risk or vulnerable groups in record time, namely 12 to 18 months from laboratory to clinic.
A final issue is that the results of the proposed human challenge studies come exclusively from the experience of younger adults, and cannot be extrapolated to the elderly, who tend to have weaker immune responses and the highest Covid-19 mortality rate. The volunteers might end up having risked their own health without truly helping those who are in greatest need of vaccine protection.
The world is overwhelmed by the pandemic. It is imperative to expedite development and approval pathways without forgoing safety and effectiveness. Ascertaining the risks intrinsic to the disease versus those of a new vaccine in specific populations — health care workers, first responders, the elderly, those with comorbidities, and the like — is essential. But acceleration should not mean forsaking ethical concerns, putting well-intentioned volunteers at needless risk, or setting back global vaccine efforts.
Michael Rosenblatt, M.D., is the chief medical officer of Flagship Pioneering, a venture firm that creates life sciences companies. He is the former chief medical officer of Merck and former dean of Tufts University School of Medicine. He serves as an adviser to Moderna, which is developing a Covid-19 vaccine; he is not a Moderna employee or shareholder. The opinions expressed are his own and do not necessarily reflect those of Flagship Pioneering or Moderna.