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Friday, July 10, 2020

Explained: What are human challenge trials, and why are they controversial?

While human challenge trials are not new, they are usually carried out in developing medications for diseases which are considered less lethal and have been better understood by scientists over the years, such as malaria.

By: Explained Desk | New Delhi | Updated: April 28, 2020 6:58:10 pm
Explained: What are human challenge trials, and why are they controversial? A person is injected as part of the first human trials in the UK to test a potential coronavirus vaccine, untaken by Oxford University, England, Thursday April 23, 2020. (Oxford University Pool via AP)

As laboratories around the world race to develop a vaccine for the novel coronavirus, many people have volunteered to take part in a controversial testing method called human challenge trials. As of April 27, a global initiative called 1DaySooner had registered 3,817 people in 52 countries who had signed up for such trials.

The method, which involves intentionally infecting volunteers with the novel coronavirus, is being promoted in order to “speed up” the process of preparing a vaccine.

How are vaccines usually developed?

In most regulatory regimes, vaccines take several years to develop, and their development typically proceeds through three phases of clinical trials.

In Phase 1, small groups of people receive the trial vaccine. During Phase 2, the clinical study is expanded and the vaccine is given to people who have characteristics (such as age and physical health) similar to those for whom the new vaccine is intended.

In Phase 3, the vaccine is given to several thousand people and tested for efficacy and safety. During this phase, participants either receive the vaccine or a placebo. The efficacy of the vaccine is determined by comparing the prevalence of infection in the group that was administered the vaccine with the one which received a placebo. The hypothesis that those in the vaccine group will be infected significantly less is thus tested.

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What are human challenge trials?

Under human challenge trials, participants of both the vaccine group and placebo group upon consent are deliberately exposed to the infection – thus are “challenged” by the disease organism.

Proponents of the method believe that such trials could save valuable time in developing a Covid-19 vaccine, as researchers would not have to wait for participants to contract the infection under real-world conditions.

A paper released on March 31 in The Journal of Infectious Diseases by researchers Nir Eyal, Marc Lipsitch, and Peter G Smith has proposed replacing Phase 3 with human challenge trials.

The paper said, “Controlled human challenge trials of SARS-CoV-2 vaccine candidates could accelerate the testing and potential rollout of efficacious vaccines. By replacing conventional Phase 3 testing of vaccine candidates, such trials may subtract many months from the licensure process, making efficacious vaccines available more quickly.”

According to experts, such testing would also require significantly less number of people than regular Phase 3 trials, which require thousands of volunteers.

As per the 1DaySooner website, “… by gathering detailed data on the process of infection and vaccine protection in a clinical setting, researchers could learn information that proves extremely useful for broader vaccine and therapeutic development efforts. Altogether, there are scenarios in which the speed of HCTs and the richness of the data they provide accelerate the development of an effective and broadly accessible Covid-19 vaccine, with thousands or even millions of lives spared (depending on the pandemic’s long-term trajectory).”

Explained: What are human challenge trials, and why are they controversial? Human challenge trials: Proponents of the method believe that such trials could save valuable time in developing a Covid-19 vaccine. (File Photo)

Human challenge trials: The ethical concerns

While human challenge trials are not new, they are usually carried out in developing medications for diseases which are considered less lethal and have been better understood by scientists over the years, such as malaria.

Critics have questioned undertaking such trials for Covid-19, a potentially deadly disease for even those who are less at risk, and which researchers are still in the early stages of studying.

In a 2016 document titled ‘Human Challenge Trials for Vaccine Development: regulatory considerations’, the World Health Organization (WHO) stated: “Human challenge studies have been conducted over hundreds of years and have contributed vital scientific knowledge that has led to advances in the development of drugs and vaccines. Nevertheless, such research can appear to be in conflict with the guiding principle in medicine to do no harm. Well documented historical examples of human exposure studies would be considered unethical by current standards. It is essential that challenge studies be conducted within an ethical framework in which truly informed consent is given.

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“When conducted, human challenge studies should be undertaken with abundant forethought, caution, and oversight. The value of the information to be gained should clearly justify the risks to human subjects. Information to be gained should clearly justify the risks to human subjects,” it added.

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