Human challenge trials

Clinical trials in which young and healthy volunteers are injected with a candidate vaccine, a month or so before being deliberately infected – or ‘challenged’ – with a live dose of a virus (e.g. SARS-CoV-2) to assess the effect of the trial vaccine.  

Challenging the participants with an infective dose of the virus under controlled conditions helps researchers study the vaccine’s effects far more quickly, by saving the time needed for the volunteers to get naturally exposed in the real world. Another advantage of challenge trials is the opportunity to experiment with several vaccine candidates and compare their safety and efficaciousness.  

Not all researchers are in favour of purposely infecting volunteers with SARS-CoV-2, a virus that has as yet no known cure. 


Infectious Disease Vaccines


Clinical TrialsDoseSARS-CoV-2VaccinesVirus