Alongside so many efforts being taken worldwide to curb the spread of COVID-19, it may seem counterproductive to ask volunteers to intentionally infect themselves with the virus we are trying to avoid; however, this is the premise of a human challenge trial.
With global pressure to find a pathway to normalcy and safety, researchers are looking for options to create a vaccine beyond traditional clinical trials, which are typically run in three phases. Phase one of clinical trials involves giving the vaccine to a small group of participants, and then in phase two, the study is expanded to a few hundred people. In phase three, the researchers give tens of thousands of participants either the vaccine or a placebo. Phase three participants are primarily studied to analyze their immune responses, so they are usually recruited from a pool of people who have a high likelihood of contracting the virus naturally. However, there is no way to control whether people become exposed and therefore, it may take months or years to see if the vaccine is effective. This is where the process deviates in a human challenge trial. Rather than waiting for natural infection to occur, if it ever does, the participants are deliberately exposed to the disease. This allows for data to immediately be collected on whether the vaccine is effective at protecting the participants against the virus and necessitates fewer people than a typical phase three trial.
Human challenge trials, if successful, could accelerate the development of vaccines worldwide. Given the rate at which COVID-19 has spread, the faster populations can be immunized, the more lives can be saved. Moreover, the availability of multiple vaccines would lessen the pressure on one supply chain and allow for greater dissemination of the vaccine.
As a second phase three trial has just been halted due to an adverse event, there are concerns around the ethics of human participation in clinical trials. Participants in traditional clinical trials bear the risk of an adverse reaction to the vaccine itself or infection through a random exposure, while human challenge trial participants are at risk through deliberate exposure. Despite the dangers, tens of thousands of volunteers have already voiced their willingness to participate in a human challenge trial as part of the advocacy group, 1Day Sooner.
Human challenge trials have been used in the past to test vaccines for diseases such as malaria, typhoid, cholera, influenza, and dengue fever. However, in any recently approved human challenge trials, medications already existed to treat participants if the vaccine proved to be ineffective. Without a guaranteed rescue for COVID-19, volunteers in a human challenge trial could be left to fight the virus on their own.
For this reason, it has been recommended that a COVID-19 human challenge trial should only include young, healthy participants who have a low risk of serious consequences from the virus. This does raise the question of whether the results of a vaccine tested only on young, healthy participants could be extrapolated to more vulnerable populations.
Britain has been in discussion with partners in the healthcare sector to begin human challenge trials, with an anticipated start date in January. In Canada, human testing has already begun through traditional clinical trials, but no human challenge trials have been proposed.
With over 2000 people from Canada indicating that they would be willing to volunteer for a human challenge trial on 1Day Sooner, there is certainly an opportunity available for challenge trials in Canada should it be determined that the risks do not outweigh the benefits. Given the chance, would you participate in a human challenge trial?