Human challenge trials are trials in which participants are intentionally challenged (whether or not they have been vaccinated) with an infectious disease organism. This challenge organism may be close to wild-type and pathogenic, adapted and/or attenuated from wild-type with less or no pathogenicity, or genetically modified in some manner.

A vaccine developer may conduct human challenge trials to accomplish one or more of a number of aims. The aims of the study determine which clinical phase the study is in. Human challenge trials are often a type of efficacy-indicating study, but most would not be considered to be pivotal efficacy studies. Almost all would be pilot in nature, performed to gain useful information to aid in the development of a vaccine. Several challenge trials might often be performed during the course of vaccine development.

Young, healthy people will be intentionally exposed to the virus responsible for COVID-19 in a first-of-its kind ‘human challenge trial’, the UK government and a company that runs such studies announced on 20 October. The experiment, set to begin in January in a London hospital if it receives final regulatory and ethical approval, aims to accelerate the development of vaccines that could end the pandemic.

Human challenge trials have a history of providing insight into diseases such as malaria and influenza. The UK trial will try to identify a suitable dose of the virus SARS-CoV-2 that could be used in future vaccine trials. But the prospect of deliberately infecting people — even those at low risk of severe disease — with SARS-CoV-2, a deadly pathogen that has few proven treatments, is uncharted medical and bioethical territory.

According to US infectious diseases expert Anthony Fauci, conducting human challenge studies are "not essential or ethically justified" at the moment as the full health impact of SARS-Cov2 infection is not yet fully understood and we have no highly effective therapies that are available to cure individuals who are infected in a challenge study.

The announcement comes just as tens of thousands of people around the world have expressed their interest in volunteering for a coronavirus human challenge study through the organization 1 Day Sooner. hVivo says it is talking to 1 Day Sooner about identifying potential volunteers.

Source: https://doi.org/10.1038/d41586-020-02821-4, edition.cnn.com