GlaxoSmithKline have announced that 300 doses of an experimental Ebola vaccine are on their way to Monrovia, Liberia. The rapidly developed vaccine has gone through phase one trials in 200 healthy volunteers across the globe to test its safety. Having passed this test it will now enter phase two trials in Liberia to test whether the vaccine is actually effective at preventing Ebola infection and disease.
How will this work?
To test vaccines, healthy people are either given the vaccine or a dummy shot. Those two groups are then followed over the course of months to record the number of individuals that go on to catch the virus or develop the disease. If fewer people in the vaccinated group catch Ebola virus than the dummy group, then we can conclude that it works. Obviously, nobody wants anyone to get Ebola in the first place (this is why we’re trying to develop vaccines, after all), but it’s necessary to tell if the vaccine is an effective tool against the virus.1
As a result, the success of the experiment is dependent upon a significant proportion of the studied people coming into contact with the virus. If nobody catches Ebola, you can’t tell whether the vaccine works. You then have nothing to aid those at extremely high risk of disease, such as family members of the already sick, or medical workers.
By all means, these vaccines cannot come too soon. If they are effective, we will have a powerful weapon against a virus that will strike again in the future.2 And clearly, the decision to send these doses to Liberia is months in the planning, it didn’t get decided overnight.
But is sending the vaccine to Liberia actually going to tell us whether the vaccine works?
A senior health minister from the Liberian government has today announced that there are just five Ebola cases left in the country. This is fantastic news and a real testament to both the national and international response to the outbreak. While not every Ebola case may be officially diagnosed in a country, the fact that new cases have been reduced to single digit numbers suggests a virus on the way out.
Taking the CDC’s cumulative case numbers (.csv download) (which can be viewed without download here) and plotting the number of cases per month, it’s quite clear where the Ebola outbreak is headed:
The virus is outta here, with cases dropping in every country (note, the January data are up until the 21st, not the end of the month). Most importantly, we can see that Sierra Leone is really the final bastion of the disease. If we want to test the efficacy of this GlaxoSmithKline vaccine, and be potentially3 ready to contain future outbreaks with it, surely it would be reasonable to retarget our efforts to Sierra Leone? While the logistics of this aren’t trivial, should we be sending a trial vaccine to a country where the chance of catching the virus is rapidly plummeting to zero? We may as well send the country thousands of sterile syringes, they’d be more useful.
- To be clear, the studied group are not then purposefully exposed to the virus to test the vaccine. Individuals already thought to be at a risk of infection, such as medical workers, are included in the study.↩
- The virus is thought to persist in insectivorous bats in the wild. When a virus persists in an animal reservoir, the only way to effectively eliminate it is to vaccinate or kill enough of that species. Both are extremely difficult and undesirable courses of action. With the virus persistent in bats, there is always the potential for human infection in the future.↩
- After all, it might not work at all.↩
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