LONDON—U.K. researchers plan to start infecting healthy volunteers with tightly controlled doses of the coronavirus in early 2021 in what they called a first-of-its-kind effort to more rapidly gauge the effectiveness of multiple vaccines against Covid-19.
The plans for so-called human-challenge trials target 18- to 30-year-olds who have been free of Covid-19 symptoms and show no other risk factors such as heart disease or diabetes, said the researchers, led by infectious-disease experts at Imperial College London, who are…