Human challenge studies are used to test the efficacy of therapeutics and vaccines, not to test the pathogen itself. I was specifically referring to the abandonment of Koch's Postulates in virology, which again has nothing to do with challenge studies where the virus is not isolated from the host.
: Due to begin in the next few weeks, it will involve up to 90 carefully selected, healthy adult volunteers being exposed to the virus in a safe and controlled environment.
: The safety of volunteers is paramount, which means this virus characterisation study will initially use the version of the virus that has been circulating in the UK since March 2020 and has been shown to be of low risk in young healthy adults.
Note that this study was in 2021, after the virus had already mutated. In order to ensure that the volunteers are infected with a specific virus version they would have to have cultured it.
: Once this initial study has taken place, vaccine candidates, which have proven to be safe in clinical trials, could be given to small numbers of volunteers who are then exposed to the Covid-19 virus, helping to identify the most effective vaccines and accelerate their development.
As shown here, the first cohort would not have been given a vaccine. But would have been used to characterize the activity of the virus on healthy humans.
> Human challenge studies are used to test the efficacy of therapeutics and vaccines, not to test the pathogen itself.
These are the same thing. The only way to demonstrate the efficacy of a vaccine is if the control group gets sick, otherwise there can't be a relative improvement.
(That's why reported vaccine efficacy goes down over time; as people naturally get the disease it appears to be relatively less effective as some of them get natural immunity.)
> These are the same thing. The only way to demonstrate the efficacy of a vaccine is if the control group gets sick, otherwise there can't be a relative improvement.
That's simply not true. A vaccine efficacy study specifically validates how well the introduction of a vaccine prevents disease, it does nothing to show the specific link between disease and the pathogen itself.
Prior studies are needed to link the pathogen to disease, and the most accurate way to do this is to first isolate the pathogen then show that introducing it to a novel population recreates the disease. After symptoms show up, if the pathogen can again be isolated from the newly infected hosts you have a pretty strong case for causation. Moving on to reproducing the results in follow up studies would go a long way. At that point you know the likely pathogenic cause and can move on to developing a vaccine based on that pathogen and run efficacy studies to see how well the vaccine works to prevent infection, disease, or transmission.
