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What are human challenge trials?

Topics Covered: Ethical Dilemmas.

What are human challenge trials?


The UK is set to conduct the first COVID-19 human challenge trials (HCT) within a month from now.

  • While human challenge trials (HCTs) have helped give important information about several diseases, some have been surrounded by controversy and questions about ethics.

The Purpose:

  • To identify the smallest amount of virus required to infect a person.
  • To help doctors understand how the immune system reacts to SARS-CoV-2.
  • To identify factors that influence how the virus is transmitted, including how an infected person transmits the virus into the environment.

First, let us understand how vaccines are developed and tested?

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

  1. In Phase 1, small groups of people receive the trial vaccine.
  2. In Phase 2, the clinical study is expanded and the vaccine is given to people who have characteristics similar to those for whom the new vaccine is intended.
  3. 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.

What are human challenge trials? How do they take place? Why is it significant?

In this, participants of the vaccine group and placebo group upon consent are deliberately exposed to the infection – thus are “challenged” by the disease organism.

  • Such trials could save valuable time in developing a vaccine, as researchers would not have to wait for participants to contract the infection under real-world conditions.
  • 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.

The ethical concerns:

  • 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 various stages of studying.
  • In 2016 , even WHO has observed that such research can appear to be in conflict with the guiding principle in medicine to do no harm.

Need of the hour:

  1. Well documented historical examples of human exposure studies would be considered unethical by current standards.
  2. It is essential that challenge studies be conducted within an ethical framework in which truly informed consent is given.
  3. When conducted, human challenge studies should be undertaken with abundant forethought, caution, and oversight.
  4. 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.

Sources: Indian Express.