In Why Human Challenge Trials Will Be Necessary to Get a Coronavirus Vaccine I asked, “What if we develop a vaccine for COVID-19 but can’t find enough patients–healthy yet who might get sick–to run a randomized clinical trial?” Exactly that problem is now facing the Oxford vaccine in Britain.
An Oxford University vaccine trial has only a 50 per cent chance of success because coronavirus is fading so rapidly in Britain, a project co-leader has warned.
…Hill said that of 10,000 people recruited to test the vaccine in the coming weeks — some of whom will be given a placebo — he expected fewer than 50 people to catch the virus. If fewer than 20 test positive, then the results might be useless, he warned.
As I wrote, “A low infection rate is great, unless you want to properly test a vaccine.” Challenge trials have issues of external validity and they take time to setup properly but they produce results quickly and they can be especially useful in whittling down vaccine candidates to focus on the best candidates.
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