The quest for a cure to the novel coronavirus has brought the Human Challenge Trials (HCTs) into spotlight, with many volunteers coming forward to be part of it. In these trials, volunteers are intentionally infected with the virus with their consent to accelerate the vaccine development process.
The Process of Vaccine Development
Vaccine development in most regulatory regimes is a slow and painstaking process that involves three critical phases of clinical trials usually carried out over several years.
The first phase, or Phase 1, involves small groups of people who receive the trial vaccine. In the second phase, known as Phase 2, this clinical study is expanded. The vaccine is administered to people with characteristics such as age and physical health similar to those for whom the new vaccine is being developed.
In Phase 3, the vaccine is given to several thousand people and tested for its efficacy and safety. Here, participants either receive the vaccine or a placebo – a substance that looks like real treatment but isn’t, such as sugar pills or saline injections. The vaccine’s effectiveness is gauged by comparing the prevalence of infection in the group that was administered the vaccine with the one which received a placebo. Consequently, the hypothesis that those in the vaccine group will contract the infection significantly less is put to test.
The Role of Human Challenge Trials
In HCTs, both the vaccine and placebo groups are deliberately exposed to the infection after their consent, thus challenging them directly with the disease organism. Such trials are usually carried out when developing medications for diseases that are considered less lethal and have been better understood by scientists over time, such as malaria.
Several scientists have proposed replacing traditional Phase 3 testing of vaccines with controlled HCTs for the Covid-19 (SARS-CoV-2) vaccine. This could speed up the testing and potential rollout of efficacious vaccines. These trials could potentially shave off many months from the licensure process, making effective vaccines available more quickly, and requiring significantly fewer people than regular Phase 3 trials.
Ethical Concerns Surrounding HCTs
Despite the potential benefits of HCTs in hastening the vaccine development process, they have been met with opposition due to ethical concerns over deliberately infecting volunteers with a disease that has yet to be fully understood and could potentially be deadly even for those less at risk.
In 2016, the World Health Organisation (WHO) emphasised an ethical framework for conducting challenge studies, stressing on the importance of informed consent. It stated that human challenge studies should be undertaken with ample forethought, caution, and oversight. The value of the information to be acquired should clearly justify the risks to human subjects.
