Ebola researchers ponder question of 1 shot or 2
Print Edition
SCIENTISTS racing to develop an Ebola vaccine are trying to determine whether they can best fight the disease with a single injection or two, a calculation that could determine how quickly and effectively a program can be rolled out.
Two vaccines, one after the other, would almost certainly give far greater protection than a single shot against the deadly virus that has killed more than 6,000 people in West Africa this year.
But it would also make mass immunizations complicated in the worst-affected countries of Guinea, Liberia and Sierra Leone, where weak health systems have all but collapsed under the weight of the epidemic.
With the epidemic growing exponentially through much of the year, the initial focus was on developing a single shot that could be tested and deployed as fast as possible.
Now, however, with disease transmission rates tailing off markedly in Liberia, there is more debate about a double vaccine program that would provide greater protection, even if it might take longer and be harder to implement.
“There is now more and more talk about what can we do to prolong vaccine protection,” said Ripley Ballou, head of Ebola research at GlaxoSmithKline.
He still hopes a single-dose vaccine will be of use in the current outbreak, but also sees a need to evaluate the “prime-boost” approach of giving a first shot to stimulate the immune system, followed by a second booster a few weeks later.
Health officials in London and Washington, as well as non-profit groups that are also helping fund clinical trials, are liaising closely on the best way forward.
A Liberia trial, involving up to 30,000 participants, will test single shots of GSK’s vaccine, a rival one from NewLink and Merck, and a placebo.
Although the Ebola slowdown in Liberia is good news, it means the trial may not see enough new cases to demonstrate the benefits of vaccination.
Other studies are starting to analyze the prime-boost approach. Johnson & Johnson expects to start testing its experimental shot with a booster developed by Denmark’s Bavarian Nordic “very soon.”
Its chief scientific officer, Paul Stoffels, said: “It is cumbersome, because you need two vaccines, but it is clear that you will get the best protection, both short and long term, from a prime-boost.”
A prime-boost vaccine will be more difficult to make in large quantities, since the booster component from Bavarian needs to be grown in chicken eggs, limiting supply. But past experience suggests it should pack more punch.
Tests of similar two-pronged vaccines in other diseases suggest the booster component can increase immune responses around 30-fold for the production of antibodies and up to 10-fold for the body’s own disease-fighting T-cells — two key elements of the ability to fight off infection — said Adrian Hill, a vaccine expert at Oxford University’s Jenner Institute.
That extra protection may be needed in West Africa, where infection with malaria could also depress people’s immune systems.
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