There are several large-scale vaccine trials going on in the U.S. right now, and many dozens more undergoing testing across the world.
The race to develop a safe and effective vaccine is one of the biggest scientific endeavors in recent memory, but some are calling for scientists to adopt a controversial practice that could speed up these efforts.
Human challenge trials can be used to efficiently test the efficacy of a vaccine by intentionally infecting study participants with the virus.
“Challenge trials are used to get a quicker signal of whether a vaccine is likely to be effective than you would get by waiting for people to get infected naturally,” said Josh Morrison, a lawyer and the co-founder and executive director of 1Day Sooner, an organization that advocates on behalf of COVID-19 challenge trials. “So in a challenge study you might have maybe 100 people, half of them get the placebo and half of them get the vaccine, versus a phase three study might be 5,000 or 10,000 people.”
Traditionally, participants in a vaccine trial may or may not get infected while living their day-to-lives, so it can take months if not years before enough participants are exposed to accumulate data on efficacy.
But there are serious ethical concerns involved in challenge trials, especially as there are many questions remaining about how the novel coronavirus affects the human body. It raises the question of whether or not it is possible for participants to have informed consent about being infected with the virus.
Additionally, in double-blind studies, a significant number of participants will be infected with the virus but will not receive a dose of the experimental vaccine at all.
“We definitely don’t want anyone making the decision who doesn’t understand what a challenge trial is and doesn’t understand that there are real risks,” said Morrison.
He argues that there are other activities that adults engage in which carry a higher risk of death than the coronavirus, such as military service, kidney donation or pregnancy. However, critics of challenge trials argue that the long term impacts of the coronavirus are still unknown, so the true risk is unknown.
Morrison argues that participants should get to decide if they feel their personal risk is worth the potential scientific gain.
Challenge studies can be limiting as typically only young and otherwise healthy people are allowed to participate, in order to reduce risks.
Morrison says large-scale phase three trials would still need to be conducted in order to ensure that vaccine candidates are safe in a wide variety of people; however, he believes challenge trials can be used at an earlier stage of vaccine development to quickly test efficacy before proceeding to phase three.