Experimental Ebola vaccine appears safe, NIH says

The first experimental Ebola vaccine to be tested in humans appears safe and capable of stimulating the immune system, according to a small, early clinical trial at the National Institutes of Health.

But the dose of vaccine required to spur the immune system into action is very high, which could make it harder for its manufacturer to quickly produce it, experts say.

Still, the results of the 20-person study, launched in September, are promising enough to proceed to a study in West Africa with thousands of participants, said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. These trials could take some time, because researchers will have to wait to see if people who are vaccinated contract Ebola.

The vaccine, developed by the NIH, uses a chimpanzee cold virus, called an adenovirus, to carry genes from two types of Ebola viruses into human cells, Fauci said. The vaccine – which will be manufactured by GlaxoSmithKline -- can't cause Ebola. It's also being tested in the United Kingdom, Mali and Switzerland.

The study found that all 20 people who received the vaccine made antibodies against Ebola, according to an article in The New England Journal of Medicine. Some people who got the vaccine also produced immune cells, called T-cells, that fight off infections.

People who got a higher dose of vaccine had a stronger immune response, the study says. The vaccine appeared safe. The only side effects were short-lived fevers in two people who received the higher dose.

Peter Hotez, dean of the National School of Tropical Medicine, said he's concerned that it took a high dose of vaccine to produce an immune system reaction. That could make it hard to produce enough of the vaccine to save lives in the West African outbreak, where Ebola has infected 15,351 people and killed 5,459, mostly in Guinea, Sierra Leone and Liberia.

The NIH vaccine appears to require tens of thousands more viral particles to stimulate the immune system than a rival vaccine, developed by the Public Health Agency of Canada, called the VSV vaccine, said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. That vaccine uses vesicular stomatitis virus, which belongs to the same family as rabies, to carry Ebola genes into cells. Commercial rights to that vaccine have been sold to Merck.

"When time is of the essence, as it is during the current outbreak, the question is not, 'Can you make the vaccine?' but 'How soon can you make? And how much?' " Osterholm said.

Thomas Geisbert, an Ebola expert at the University of Texas Medical Branch in Galveston, expressed another concern.

In animal studies, the NIH vaccine didn't protect for very long, and required a booster to provide long-lasting protection.

Although scientists have been working on Ebola vaccines for years, it wasn't until the outbreak in West Africa that large pharmaceutical companies showed interest in developing vaccines and bringing them to market, Geisbert now.

Now, nine Ebola vaccines are being tested, Fauci told Congress last week.

The NIH and Canadian vaccines are the furthest along.