Here’s Everything You Need To Know About The COVID-19 Challenge Trials

More than 140 organisations around the world are working to develop a safe and effective COVID-19 vaccine. As of today, 12 vaccines are in late stage phase 3 clinical trials and together recruit thousands of volunteers worldwide.

In reality, the truth is that most of the COVID-19 vaccines in clinical trials (Phase 1/2/3) right now may fail. This is because for a vaccine to get full approval, they must pass the many hurdles, and consistently prove that they are safe and effective. Vaccines have a higher regulatory bar to pass — this is because they are delivered to otherwise healthy individuals en masse. For more on the process of vaccine development, check out our previous post here.

Vaccines have a higher regulatory bar to pass — this is because they are delivered to otherwise healthy individuals en masse. #TSMUpdates #COVID19 #ChallengeTrials

When will we have a coronavirus vaccine? Well.. that’s a good question! Unfortunately any answers anyone has on this question are tentative. A number of vaccine developers hope they are able to develop a vaccine by the end of 2020. For the latest updates on the vaccines in Phase 3 clinical trials, check out our weekly newsletters here and feel free to sign yourself up.

There are a two main ways in which we can test the efficacy of vaccines. One method is being used more commonly than the other.

  1. The first method is what we see worldwide: we administer the vaccine to a number of people and follow them closely.
    Every couple of days/weeks, the volunteers are tested for COVID-19 – have they been infected in their day-to-day lives?
    Their bloods are also taken to check if they are developing antibodies against the virus?
  2. The second method has more ethical considerations. Here, volunteers are given an experimental COVID-19 vaccine candidate and then deliberately exposed to the novel coronavirus (SARS-CoV-2), which causes COVID-19. This method will directly check whether the vaccine has been effective.

There are 2 main ways of testing vaccine efficacy: 1. Administer the vaccine to people + follow them closely as in Phase 1/2/3 clinical trials. 2. Via human challenge studies, where volunteers are deliberately infected by the pathogen.


An Introduction to Human Challenge Trials

What are human challenge trials?

The second method listed above is what a challenge trial is. According to the World Health Organisation‘s (WHO) regulatory considerations, “human challenge trials are trials in which participants are intentionally challenged (whether or not they have been vaccinated) with an infectious disease organism.”

The WHO document further states that, “This challenge organism may be close to wild-type and pathogenic, adapted and/or attenuated… with less or no pathogenicity, or modified in some manner.”

In another COVID-19 centric document, the WHO defines challenge trials as “Controlled human infection studies [that] involve the deliberate infection of healthy volunteers”.

The @who defines challenge trials as “controlled human infection studies [that] involve the deliberate infection of healthy volunteers”. #TSMUpdates #COVID19 #ChallengeTrials

What are the advantages of human challenge trials?

  • These trials can be substantially faster to vaccine field trials
  • They can be used to compare the efficacy of multiple vaccine candidates and select the most promising vaccine for larger studies and also for manufacturing purposes.
  • Ensures that vaccines that are ultimately deployed are more effective

The Ethical Considerations of Challenge Trials

  • There is concern that some volunteers will participate without fully knowing the risk because of the monetary award.
  • The researchers must ensure that the participants understand the risks and limitations to the trial.
  • Since these trials will be conducted on young healthy individuals, concerns are raised that they may not reveal important information for older and high-risk individuals.
  • Not a lot is understood about the SARS-CoV-2 virus and how it causes COVID-19.
  • We are not 100% certain on the long term effects of exposure to the virus.
  • Although death in healthy young individuals is lower, it cannot be ruled out.

According to an interview conducted by the BBC, Prof Julian Savulescu, an expert in ethics at Oxford University said that the trials were justified: “In a pandemic, time is lives. So far, over a million people have died”. Given the high stakes and daily death rate of more than 1,000 people, Prof Savulescu believes that is is unethical not to conduct challenge studies. Studies that will give us vital information on how best to manage the COVID-19 situation worldwide.


What Do We Know About the COVID-19 Challenge Trials?

Why are these trials being considered?

It is widely understood that a vaccine will help bring the world one step closer to normalcy. These trials will encourage accelerated vaccine development and ensure that the most effective vaccine candidates be identified and ultimately become available. This is essential as globally, we only have so much capacity to develop vaccines – we don’t want to waste our resources on a vaccine that may not work. In addition to this, the COVID challenge trials will help us understand more about the SARS-CoV-2 virus’ mode of COVID-19 infection and transmission.

When will these trials begin?

The world’s first COVID-19 human challenge trials are to begin in London at the start of the new year (2021). Up to 90 fit individuals aged 18-30 years will receive coronavirus vaccines.

A month or so later, the volunteers will receive tiny doses of the novel coronavirus, SARS-CoV-2, via the nose. According to the Financial Times, these doses of the virus will “gradually be increased until they reach a level that reliably infects the upper respiratory tract”. This process is called dose testing.

The human COVID-19 challenge trial in London, UK aims to identify a suitable dose of the SARS-CoV-2 virus that could be used for future COVID-19 vaccine challenge trials. In other words, the researchers will be trying to find out the lowest possible dose required for the virus to take hold and cause COVID-19 infection in humans. If we don’t know this value, we don’t know how much of the virus to expose the human challenge trial volunteers to. We don’t want to expose the volunteers to too much of the virus, or too little — the dosage must be just right.

When do we hope to see results from the challenge trials? Do we have a timeline?

According to Nature News, the exact design of the study has not yet been finalised. It is possible that some volunteers will be given placebo injections instead of the vaccines, but it could also be that all volunteers receive different COVID-19 candidate vaccines for a comparison. The question of what vaccine candidates will be used for the human trial studies are still to be determined.

Where can I sign up for the COVID-19 human challenge trials?

To sign up for the dosing study in London, you can sign up here.

To sign up for the human challenge trials, you can register with 1DaySooner here. To date, 1DaySooner has upwards of 38,500 volunteers signed on from 166 countries.


Lastly, we would personally like to thank all volunteers partaking in COVID-19 vaccine trials around the world. It is a brave step with unidentified potential risks. We wish you all the best!

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