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Ebola Vaccine Trials Forcing Tough Choices
An anonymous reader writes: Medical researchers hope an experimental vaccine for Ebola can help protect against infection and slow the spread of the disease. Efficacy trials for the vaccine begin in a few months, and it's forcing some difficult decisions for health care officials. The first test will involve front line health care workers, who, as a group, are at the gravest risk of infection. But every trial needs a control group, and scientists are bitterly divided over whether the vaccine should be withheld from a portion of those putting their lives on the line to protect the rest of us. Development of the vaccine has been vastly accelerated already, due to the virus's spread and its mortality rate.
"The leading alternative is a design known as step-wedge, which essentially uses time to create a control group. In this design, researchers take advantage of the inescapable reality that large-scale trials can't give everyone the vaccine on the exact same date; they compare the rates of infection in people already vaccinated with those who have yet to receive the shots. Barney Graham, a virologist ... says "people are more comfortable" with the step-wedge design, because everyone in such a study would get the Ebola vaccine. But statistically speaking, this design makes it more difficult to determine the vaccine's worth, and it takes longer." NY Mag has a related story summarizing the treatments currently being used to fight Ebola.
"The leading alternative is a design known as step-wedge, which essentially uses time to create a control group. In this design, researchers take advantage of the inescapable reality that large-scale trials can't give everyone the vaccine on the exact same date; they compare the rates of infection in people already vaccinated with those who have yet to receive the shots. Barney Graham, a virologist ... says "people are more comfortable" with the step-wedge design, because everyone in such a study would get the Ebola vaccine. But statistically speaking, this design makes it more difficult to determine the vaccine's worth, and it takes longer." NY Mag has a related story summarizing the treatments currently being used to fight Ebola.
They known the mortality rate of ebola when untreated.
They can find out the mortality rate effect when vaccinated.
It isn't that simple. The situation on the ground is changing rapidly over time, so current rates are worthless as a point of comparison.
Compared to many diseases with which we're familiar, Ebola is rather difficult to transmit, given that someone needs to be in contact with the bodily fluids of an infected individual. As such, infection rates among the population of medical staff are highly dependent on the conditions of the environment. A properly maintained quarantine with medical professionals engaging in best practices should basically have a 0% infection rate, whereas the sorts of conditions they're seeing in Africa right now will see significantly higher infection rates among the medical staff, but even those rates can vary significantly from facility to facility depending on the facility's resources, the level of training of the staff and their assistants, and how cooperative the patients are. As those infection rates change, so too do the mortality rates. Moreover, as I mentioned, those rates are likely changing over time as new practices are put into place, training is improved, resources are improved thanks to new funding, or changes occur in the cultural awareness of the patients.
Which is all to say, you need some way to account for the changes to the mortality rate that are occurring for reasons besides the vaccine. Comparing future mortality rates against past rates doesn't do that. All that does is tell us that something has changed, but it doesn't tell us what changed. You need a control group in the same environment going through the same changes, with the only difference being that the test group is vaccinated. Anything else, and we'll have no way to isolate the efficacy of the vaccine or its lack thereof from the other changes occurring in the environment that are also affecting the outcome.
One problem with rushing a treatment to market (aside from the obvious side effects and toxicity risks) is that you sometimes end up with a treatment that works but you have no idea why it works. This has happened with some drugs in the past. We've started testing them and found that they worked really well. So we stopped the clinical trials early in order to rush the drug to market quickly for perfectly appropriate humanitarian reasons. After all if you have a drug that you know works then it's pretty cruel to withhold it from someone who would benefit. The problem is that sometimes we know a drug works before we know why or how it works.
Part of clinical trials is figuring out if a treatment will work. The other part which is sometimes even more important is figuring out why a treatment works so that we can build off that information in the future. If you skip or stop clinical trials early you sometimes end up losing this critical information. If we don't know why something works it's pretty hard to make further progress in developing even better treatments.
The point is... while this epidemic is going on, it will be very hard to control the study. Most Ebola outbreaks affect less than a few hundred people. There are enough people in Africa infected now that if you limit access to this Vaccine a whole cottage industry will likely spring up around it. Just like it did over AZT in the 80s. Do YOU want to be the healthcare worker guarding the stash of drugs that's the only hope for survival to the teaming throngs surrounding your clinic?
Give it to everyone, hope for the best, when the worst is over start your study.