Why federal government should reject human challenge trials for COVID-19 vaccine


This column is an opinion by Françoise Baylis and Landon J. Getz. Baylis is University Research Professor at Dalhousie University in Halifax, a member of the Order of Canada and the Order of Nova Scotia, as well as a fellow of the Royal Society of Canada and of the Canadian Academy of Health Sciences. Getz is a Ph.D. Candidate, Vanier Scholar and Killam Laureate in the Thomas Lab, Department of Microbiology and Immunology at Dalhousie University. For more information about CBC’s Opinion section, please see the FAQ.

There are 12 vaccines for COVID-19 in conventional Phase 3 trials, and the interim results for three of these are promising. On Nov. 9, Pfizer and BioNTech announced that their trial shows more than 90 per cent effectiveness in preventing COVID-19. Two days later, Russia announced that its vaccine, SputnikV, is 92 per cent effective at preventing infection. And Moderna announced Nov. 16 that its vaccine is 94.5 per cent effective.

Although the relevant data have not yet been released for public review, there is reason to be hopeful that safe and effective vaccines are well on their way. Canada has pre-ordered 20 million doses of both the Pfizer-BioNTech and Moderna vaccines, with options to buy more.

But for some, vaccine development isn’t happening fast enough.

On Oct. 22, Marcus Powlowski — the Liberal Member of Parliament from Thunder Bay-Rainy River, a former ER doctor, and a champion of COVID-19 vaccine challenge trials — presented an e-petition to the House of Commons urging the federal government to approve such a trial. The government is required to respond within 45 days.

The Canadian government should reject this proposal for human challenge trials and stay the course on vaccine development.

Interim analysis suggests COVID-19 vaccines from Pfizer and Moderna will work, but final results, expected later this year, are necessary to confirm, says epidemiologist Dr. Christopher Labos.   5:40

With a conventional trial, thousands of volunteers are given a vaccine that is in development, and thousands more are given a placebo. They all go about their daily lives, and over time researchers can see whether those who were vaccinated get sick less often than those who were not vaccinated.

In contrast, a human challenge trial for COVID-19 would involve the deliberate infection of healthy volunteers.

The purpose of such a trial is to accelerate vaccine development. With a human challenge trial, fewer research participants are needed (perhaps as few as a 100), and less time is required. This is because researchers don’t need to wait for chance encounters with the virus. The participants are exposed to the virus, isolated in a research facility for two to two-and-a-half weeks, and observed to see who gets sick. On this basis, researchers can assess whether the candidate vaccine works.

In defence of the proposal to purposefully infect young people (aged 18 to 30) with SARS-CoV-2, the virus that causes COVID-19, the e-petition written by the non-profit 1Day Sooner and presented to the House by Powlowski states, “The risk to young healthy volunteers is on par with other acts of public service, such as living kidney donation.”

In addition, according to Powlowski, “Young people from across Canada are ready to step-up to serve their country in our war against COVID-19.” In response to those who say vaccine challenge trials are unethical, he asks a rhetorical question: “If it’s unethical to allow people to assume that risk, wouldn’t it be unethical to allow police to go into a situation where they could be harmed?”

But is it reasonable to expect such sacrifice on the part of Canadian youth?

Trial kits for Pfizer’s COVID-19 vaccination study are seen at the Research Centers of America in Hollywood, Fla., on Sept. 24. (Marco Bello/Reuters)

In addition to this contextual concern, there are a number of discrete problems with the proposed Phase 3 challenge trials.

While human challenge trials have been used in vaccine development before, typically this has been done when there is available “rescue medication.” This means that if a healthy volunteer becomes seriously ill as a result of intentional infection, they can be treated effectively.

However, there is still no effective treatment for COVID-19.

In addition, evidence shows that there is potential for long-term lung and heart damage associated with severe infection. Although the volunteers would receive the smallest possible dose of the virus to elicit an infection, there is the possibility that some volunteers will respond more severely than others.

Staff are seen Sept. 29 setting up a production line in Visp, Switzerland, where the Moderna mRNA coronavirus disease (COVID-19) vaccine will be produced. (Denis Balibouse/Reuters)

Deleterious cognitive effects have also been documented as a result of COVID-19 infection. For example, one study indicated that people younger than 50 years old are seven times more likely to suffer a stroke as compared to infection with a typical flu virus. With no effective treatment, severe infection could mean disability, or worse, death.

Another concern is the problem of extrapolation.

The population most at risk from COVID-19 includes older persons and those with underlying medical conditions. With conventional vaccine trials, research is done in a much larger group, including those most at risk. The proposed challenge trial would infect healthy young people to minimize the risk of harm to research participants. This choice of target population introduces a technical problem, insofar as the virus does not appear to behave the same way in different groups.

The decision to target young people highlights yet another issue. Importantly, youths are generally less risk averse. With one in four Canadian youth not in education, employment or training, according to Statistics Canada, and with potential compensation for research participation as high as $7,000 based on experience in the U.K., there is a clear risk of undue inducement.

For these reasons, and with a number of promising vaccines in conventional Phase 3 trials, the federal government should reject the petition calling on it to “publicly announce a plan for COVID-19 human challenge trials.”




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