Representative image of a person getting vaccinated. Photo: Unsplash/National Cancer Institute.
New Delhi: Dr Gagandeep Kang, a professor of microbiology at the Christian Medical College, Vellore, has said that despite numerous risks, it is worthwhile to conduct human challenge trials as they could help design better treatments and vaccines.
According to a report in the Financial Times, the world’s first human challenge trial will commence in London in January – where participants will be vaccinated with a candidate vaccine and subsequently exposed to the novel coronavirus after a month or so. This constitutes the ‘challenge’: to confront the vaccine with a live SARS-CoV-2 virus. Close to 38,000 people from 166 countries have already volunteered to participate.
Previously, human challenge trials, performed with thousands of participants, have helped accelerate the development of vaccines against typhoid and cholera. In an interview with The Hindu, Kang stressed that such studies are frequently undertaken to test vaccines and understand infection and disease.
She cited the example of a norovirus infection, where – thanks to the absence of any animal models – human infections were the only way to study the disease for 30 years. With SARS-CoV-2, human challenge trials could shed light on several aspects of the virus – including the infectious dose, the kinetics of the immune response and susceptibility to disease, according to her.
When The Hindu asked her what measures could be taken to ensure the viral strain caused only mild infections in the trial, Kang said SARS-CoV-2 caused a significant number of asymptomatic infections, so the mildness of the infection depended on the host and not the virus. But in the absence of definitive treatment options, she said the human challenge studies would include only young, healthy people who had a minimal chance of developing a severe form of the disease.
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However, Kang also said there were also risks with testing a vaccine in a younger population – given that several young people have also needed to be hospitalised and that many studies have shown that many of those who recover suffer longer term complications.
“So the question is – should we wait until we have a definitive treatment — like the anti-malarials that are used in the controlled human malaria model that is now almost a requirement for all malaria vaccine candidates?” she asked.
“The risks may be small but they exist,” Kang said, pointing out that thousands had stepped forward to participate in such studies for the benefit of society. “So we could equally ask, should we stop them from contributing as long as they understand the risks and investigators make sure that the highest quality clinical care is provided?”
Kang also said that since the human challenge trial only studied young, healthy participants, its results wouldn’t be representative of an older population and those with comorbidities, since it wasn’t possible for the study to represent “every facet of infection or illness in the human population”. She also said, for this and other reasons, these challenge trials aren’t a replacement for phase 3 clinical trials.
“If a [controlled human infection model] is used for down-selection, you will be progressing a vaccine … based on a few hundred people in a short timeframe, whereas taking the same candidate to a full phase 3 will require, given the size of current trials, at least 30,000 people, who may participate in a trial for a vaccine that may or may not work,” she explained.
Regarding remdesivir, an antiviral drug that has been used as a ‘rescue remedy’ to prevent participants from progressing to serious illnesses – Kang said that while it had shown no substantial mortality benefits, there wasn’t anything better available either.