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What is a “human challenge trial,” and could it solve the coronavirus vaccine problem?

  • A volunteer is intentionally infected with a disease to help find a vaccine
  • Human challenge trials have helped vs. malaria, typhoid, and influenza
  • Some, though, say it’s unethical to conduct such trials. 

More than 10,000 people from 52 countries have volunteered to be intentionally infected with COVID-19 to speed up the development of a vaccine, according to advocacy group 1DaySooner.

1DaySooner is in favor of human challenge trials, which the World Health Organization defines as trials where researchers intentionally infect participants with an infectious disease organism. Human challenge trials have helped find vaccines for influenza, malaria, typhoid, dengue fever, and cholera. 

The advocacy group isn’t alone, either. On April 20, 35 members of Congress proposed the use of human challenge trials in a letter to the Food and Drug Administration and the Department of Health and Human Services. 

Vaccine development typically consists of four testing stages. In the first stage, scientists test the vaccine on animals and less than 100 human volunteers. If the results are right, the scientists next test the vaccine on a few hundred human volunteers in phase 2. 

1DaySooner says phase 3, in which thousands of human volunteers receive the vaccine, usually takes the longest because scientists have to wait for volunteers to become naturally infected with the virus. The group advocates that exposing volunteers to COVID-19 “under highly controlled conditions” could speed up phase 3 and get the vaccine to phase 4—where it is widely distributed to the public—quicker. 

The advocacy group’s statistics argue that finding a vaccine just one day sooner could save 19,500 lives. If human challenge trials speed up the process by a month, it could save more than a half-million lives. 

Of course, volunteers infected with COVID-19 still run the risk of death, which is why human challenge trials are considered unethical by some critics. Most diseases that have used human challenge trials to speed up treatment development were not as lethal as COVID-19’s death rate, according to Vox. 

“Such research can appear to be in conflict with the guiding principle in medicine to do no harm,” the WHO said. “Well-documented historical examples of human exposure studies would be considered unethical by current standards.” 

To combat those concerns, the WHO says these trials should be “undertaken with abundant forethought, caution, and oversight” and “the value of the information to be gained should clearly justify the risks to human subjects.” 

1DaySooner says scientists can minimize these risks by ensuring that all participants are between the ages of 20-45 and have no underlying health conditions. The group also wants to enroll volunteers who are already likely to be exposed to COVID-19 and to isolate them in highly controlled environments under constant observation. 

A study published on March 30 found that only 0.031% of people in their 20s infected with the virus have died, including people with underlying conditions. Vox pointed out that’s similar to the risk of death from a living kidney donation, which is a widely allowed surgery. 

In addition to health risks and ethical concerns, there’s also the chance that human challenge trials wouldn’t speed up the process, vaccine researcher Myrone Levine told the New York Times. Because infections are still rising rapidly around the world, Levine argues scientists will have plenty of candidates naturally exposed to COVID-19, so there’s no need to infect anyone intentionally. 

Currently, there is no vaccine for COVID-19 approaching phase 3 of the development—although there are dozens of vaccines now in progress

Sources: 1DaySooner, WHO, VOX, Milken Institute, New York Times, The Lancet


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