Human challenge trials (also called human challenge studies and human infection studies) are clinical trials that involve deliberately exposing willing volunteers to an infectious disease. Human challenge trials have been used for several diseases, including influenza, typhoid fever, cholera, malaria and, more recently, COVID-19.
Further reading
Wellcome (2018) What are human infection studies and why do we need them?, Wellcome, December (updated 28 June 2021).