The race for a COVID-19 vaccine is hotting up. There are currently over 150 candidate vaccines in development around the world, with around 30 being tested on humans.
But for some scientists, the progress isn’t fast enough. There are growing calls for so-called ‘human challenge studies’, which would deliberately infect volunteers with the coronavirus SARS-CoV-2, with the aim of speeding up vaccine development by, according to one paper, as much as several months, potentially saving thousands of lives.
This would be a big ethical leap from current vaccine trials. Currently, a candidate COVID-19 vaccine goes through three phased trials. In the final trial (phase III), up to 10,000 volunteers are given either the candidate vaccine or a placebo. The volunteers then go about their daily lives, and the scientists wait to see who gets infected, and who doesn’t. If the vaccine works, the scientists should see significantly fewer COVID-19 cases in the vaccine group than in the placebo group.
The downside of this approach is that it takes time for volunteers to become infected, especially in countries with falling case numbers. Human challenge studies could potentially speed up the process by giving the candidate vaccine to a much smaller group of volunteers, and then, once the vaccine has triggered an immune response, directly infecting them with the virus. The scientists would monitor how the volunteers respond to the virus, gathering real-time data on the vaccine’s effectiveness.
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