Story highlights There is "extraordinary" rush to develop Ebola vaccine, says scientist Adrian Hill

Ethical questions arise in regard to when widely distribute vaccine, says Hill

Hill: There are risks in rushing and risks in delaying

The "extraordinary" rush to develop an Ebola vaccine is moving forward apace, the lead researcher told CNN's Christiane Amanpour on Tuesday, adding that the fast pace may engender ethical concerns about how it the vaccine is eventually implemented.

"This is, frankly, extraordinary," Adrian Hill of the Jenner Institute at Oxford University said. "We are trying to do in a few months something that might typically take 10 years. We've had accelerated reviews of all our applications, regulatory and ethical approvals, and so on."

"And we're now trying to proceed so quickly that if things go well, by the end of the year, this vaccine might actually be being used in the three affected countries in West Africa."

He said that the vaccine has been shown to be "really quite remarkably protective" in studies on monkeys at the National Institutes of Health in the U.S.

Researchers are under tremendous pressure to develop a vaccine, as over 3,400 people have died in West Africa and a Spanish nurse's assistant was confirmed on Monday to be the first person to have contracted the virus outside of Africa.

But even if researchers are able to make enough vaccine, and have data showing that it is safe for use in humans and produces good immune responses, Hill said that they will would not know that "it actually works."

"So we're going to have to figure out a way of using the vaccine, and at the same time evaluating it. And there's a great deal of discussion about how you might do that now."

Therein may lie ethical concerns.

There is little worry, he said, about administering a vaccine to humans in a phase one trial, as he said will begin this week in West Africa. The issue is what you do after that.

"Once you've shown safety in those individuals, do you go on to deploy the vaccine in a very large population -- ideally of health-care workers who are at greatest risk -- without knowing that the vaccine actually works?"

"Or instead, do you wait several months -- maybe six months, maybe a year -- to prove absolutely that the vaccine has a certain efficacy and then start thinking about deploying it widely?"

"And if you wait that long, the epidemic might either be over, or the whole thing might be completely out of control."

"So that's the challenge -- to figure out what the best thing to do, given those conflicting priorities as I've described them."