In a normal clinical trial for a vaccine, a person in the vaccination group is given the vaccine while those in the placebo group get something like a saline injection. Both groups then go out to the community. Observations are made over time in both the vaccine and placebo groups to determine whether the vaccine protects people from infection.
There’s another kind of trial which speeds things up a lot called a “Challenge Trial”. That’s when a person is vaccinated and then is later intentionally exposed to the virus to see whether they get sick.
There are obviously some ethical questions about challenge trials but they have some real advantages as well because they can speed up getting results by weeks or even months. You get cleaner data as well because you are sure about the exposure. So, in a public health emergency – when people are losing their lives every day- should we be using Challenge Trials to speed things up? After all, you know for sure that people are dying every day and that if you can speed up the trial, you’ll be able to save many lives by accelerating the trials.
Persons in Challenge Trials are volunteers. They are also done after the Phase II trial has been completed so you have at least some information about the safety.
On the other hand, you may need to challenge persons that got the placebo (not the vaccine)… posing clear ethical questions. An alternative could be to challenge just the vaccine group (not the placebo group) with various doses of challenge virus and look to see whether there’s a dose-response. That might be a way around exposing the placebo group.
Anyway- take a look at this essay about Challenge Trials in Medscape this week. Interesting short read.
