Study Results May Be Giving False Hope
Facing a disease epidemic that would likely kill you if you contracted it, or being injected with a vaccine that has not had adequate research into efficacy and long term safety; what would you choose? This is the dilemma surrounding the Ebola vaccine.
A recent study published in the prestigious medical journal, The Lancet, suggested that the new Ebola vaccine was “100 percent effective.” Many people would take their chances with a vaccine when facing an epidemic as horrific as Ebola, which is possibly why the media praised it like it did. Forbes called the Ebola vaccine a “Christmas gift.” National Public Radio (NPR) wrote, “Now it looks like such a large outbreak is unlikely to ever happen again. Ever.” Sounds pretty amazing right? However, if you’d take the time to actually read the study on the Ebola vaccine, you’d get a much different picture.
In Guinea, West Africa, during the 2015 Ebola outbreak, the Merck Ebola vaccine (rVSV-ZEBOV) entered phase III efficacy testing. One group of people exposed to Ebola was given the vaccine two-three days after exposure, while the other group was given a vaccine three weeks later. The group who got the vaccine immediately reported zero cases of Ebola while the delayed group reported 16. The vaccine’s early success made the healthcare workers administer the vaccine to all patients who had been exposed to Ebola.
Although this seems like it was the best option, morally, considering the effect the vaccine was having in preventing Ebola in exposed individuals, it also reduced the amount of statistical data available. There’s no way to gain enough statistical data to know how truly effective the vaccine is until, perhaps, another outbreak occurs.
The Ebola epidemic had already begun to wane as trials began, and certainly numbers of infected patients were going down before the delayed vaccination group received its vaccination. This begs the question of whether Ebola cases were slowing down due to vaccine or the waning epidemic. It’s hard to say for sure, due to the small and incomplete amount of data.
Semantics and Vaccine Efficacy
That 100 percent effective statistic lauded by media outlets may be misleading. Such outlets tend to report the relative risk of a vaccine or medical treatment instead of the absolute risk. The relative risk is what the risk of getting a disease is compared to another group (vaccinated versus unvaccinated). The absolute risk is an individual’s risk of getting a disease over time.
For example: If a disease typically affects 10 out of 100 people and a new vaccine boasts a 50 percent effectiveness rate you might assume that this vaccine protects 50 percent of the population or 50 out of 100 people. However, the truth is a 50 percent effectiveness in relative risk means that 50 percent of the people who actually get sick are protected. In this case it’s five of the 10 sick people or five out of 100 total. That means this particular treatment only reduces any one person’s chances of getting this disease by 5 percent.
Now let’s look at the Ebola vaccine statistics:
The 100 percent effective statistic is a relative risk statistic that comes from the fact that zero (out of 2,014) people developed Ebola symptoms in the immediate vaccination group versus 16 (out of 2,380) in the delayed group.
However, in the group of people who were assigned to get the vaccine immediately but didn’t (too young, breast-feeding, or declined to participate) only eight got Ebola (out of 2108). If we assume that the vaccinated group would get Ebola at a similar rate, the vaccine only protected about eight infections in a group of 2,014, less than 5 percent absolute risk reduction. Even if we use the delayed vaccine group’s data there’s only protection for 16 people out of 2380 which is less than 1 percent risk reduction. You can see where more research is needed to see how truly effective this vaccine is.
Ebola is a particularly nasty disease, violently killing people within 16 days, so this efficacy may be enough to warrant using the vaccine even if it only works for reducing a person’s risk of contracting Ebola by 1 percent or less. But the media certainly chose the more sensational approach by divulging statistics. Another thing to consider is vaccine safety which can greatly change whether a 1 percent reduction in chances of contracting Ebola is worth the potential side effects, such as arthritis and joint pain which was found in 22 percent of participants of one study.
Potential Vaccine Failure?
Researchers eliminated participants who got sick before 10 days post vaccination (presumably because the “usual” incubation period is 10-21 days, though it can be as few as two). The reason? They were assumed to already be sick. However, experts question whether those, or some of those, who were not included actually represented vaccine failure.
Nine people in the immediate vaccination group developed Ebola in less than 10 days after vaccination – and the research team didn’t count this as vaccine failure because usually the incubation period is 10-21 days. The researchers believe those people must have gotten Ebola before the vaccination, so they didn’t count them – but that’s not at all clear. Some of the nine may have been failure of the vaccine to protect.
If even one or two of those cases were actually vaccine failure the efficacy of the vaccine drastically changes.
The news media is touting a 100 percent effective vaccine while experts look at the trial as good preliminary work that requires more research. According to Dr. Selanikio :
Even the researchers themselves, in the Lancet article, conclude, ‘The results add weight to the interim assessment that rVSV-ZEBOV offers substantial protection against Ebola virus disease.’
I’d say that statement is 100 percent true, because of the qualifiers (interim, substantial, add weight), but it’s clear they don’t think it’s time to stop evaluating this vaccine. The big problem is that it’s going to be pretty much impossible, now that Ebola has waned again, to get enough people enrolled in future studies – at least until the next outbreak.
Ebola Vaccine: 100 Percent Effective Or 100 Percent Lucky?
Typically, after a trial as successful as this one, researchers would set up a placebo controlled trial to show, without doubt, that the vaccine works. Without a placebo controlled trial, it’s hard to know for sure what caused the decrease in cases of Ebola. Could the delayed vaccine group have lived in less sanitary areas? Maybe they had fewer supplies or different burial practices.
According to Timothy P. Lahey, associate professor of Medicine, Dartmouth College:
The study investigators took meticulous steps to prevent each of these problems, and they argue persuasively that it is unlikely the protection they saw from rVSV-ZEBOV was entirely due to chance. I agree. The point is that it is easy to imagine ways the vaccine is far less than 100 percent effective, and even possible (if unlikely) the vaccine provided no protection whatsoever.
It’s unlikely that we will see a placebo trial for the Ebola vaccine, however. Experts generally agree that it would be unethical to withhold a potentially lifesaving vaccine from people who need it. Upon its apparent success in Guinea, a placebo trial is even less likely to occur.
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Ethics And Further Research
In 2014, The World Health Organization (WHO) convened a panel discussion on the ethics surrounding giving unproven interventions to those affected by the outbreak. They concluded that, “it is ethical to offer unproven interventions with as yet unknown efficacy and adverse effects, as potential treatment or prevention” which they qualify by saying “in the particular circumstances of this outbreak, and provided certain conditions are met.”
The WHO panel discussion also concluded:
There is a moral duty to also evaluate these interventions (for treatment or prevention) in the best possible clinical trials under the circumstances in order to definitively prove their safety and efficacy or provide evidence to stop their utilization. Ongoing evaluation should guide future interventions.
Though the vaccine will be under “ongoing evaluation” as the panel discussed, there are still many unknowns. Are there long term side effects? Does the vaccine provide long term protection? How effective is it really? The early success of the vaccine puts it in a position of being the only defense against another outbreak so we aren’t likely to answer these questions until the vaccine has been used and evaluated many times over. Will the vaccine save many lives or cause many unreasonable side effects? We’ll have to wait and see.
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